Is there something wrong with my bunny?

We recently got a new bunny, he's a mini lop names buddy, and he's 9 weeks old.
He's tiny! He weighs 280g. (Is this normal?)

I noticed his urine today, it was milky (greeny/yellow) but very very milky. And it smells a little fishy. And he doesn't seem to be cleaning himself properly. He has some little dreads on his tummy and his bum is pee stained and fur looks as though it's starting to become matted.
I tried giving him a little bum bath with only water (I didn't have any suitable shampoos atm) and it didn't really help.

Aside from this he is lively and appears to eat and drink enough.
Should I be concerned?

He looks much younger then 9weeks.....
Please dont bath him either. Use a warm damp cloth if you must but he looks far too delicate right now to handle baths. Whats his diet like?

He was a pet shop bunny (not the best decision) so they may have given me incorrect information I guess?
His diet is predominantly hay, a little greens and muesli, but only a touch.
I suspect someone in the household may have been over feeding him pellets and so I've made sure that I am the only person feeding him now so I know what he is eating. Is there any particular signs that may tell you how old he is or is that hard to determine?

Can you provide some better photos please? Im guessing a lop of some sort with those ears, did they say if hes a mini or Holland/dwarf? He honestly look 4-5weeks old but I am not a breeder and don't have experience with a bunny that young past my own and even she looked older then that.
Hes just got that still with mum baby look to him.

Being a petstore bunny, it's doubtful he had the full 8 weeks with his momma. It would be best to avoid greens of any kind until he's about 12 weeks of age. For now, it is best to feed plenty of hay and a plain pellet (nugget? in the UK). The mueslis or mixes are not healthy at all. He should have a plain pellet and he should have as much as he wants until he is older. Limited pellets are recommended for adult rabbits, but babies need the extra nutrition and calories of the pellets.

Here's a food comparison chart to help you choose a healthy pellet type:
http://www.therabbithouse.com/diet/rabbit-food-comparison.asp?diet=young&sortby=FoodBrand#chart

Thanks for your responses, I appreciate any advice.
Here's a few more.

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He was bought home by my sister (17) while I was at work, which I feel was a little irresponsible. She picked him because of how tiny and cute he was, he's a supposedly a mini lop btw, but nothing seems quite right and I did suspect that his age was questionable when I compare him to my other mini lop, who is supposedly only 3 weeks older and is easily 3-4 times the size. As I said, he now weighs 300g, now.
I fear that maybe he's been taken from his mother too young.

Thank you so much for your input 'blue eyes', I will adjust his diet. I wasn't aware that at this age the diet should be a little different.

That is not an 8 week old rabbit. I would say 5 weeks, maybe 6 at the most. Which means it will be more prone to digestive problems developing. You will need to be careful with it's diet. It would be best to not change his pellets right now and to stick with the ones he is used to, preferably what he had at the pet store if you haven't put him on a new pellet for more than a day or two, and he is having normal poop pellets with no mushy poop. If you do increase his pellet amount, it needs to be done very gradually over a couple weeks. I personally would not feed unlimited pellets to young rabbits, as this can very easily cause digestive issues for them, but I do feed them more than an adult if they aren't having any digestive issues from the pellets. I will feed enough that they run out of pellets about 3 hours before their twice daily feeding, then they can snack on hay til their next feeding. If there are any signs of digestive upset or mushy poop, you will need to decrease the pellet amount until it stops, then try to increase the amount more gradually.

I agree to not introduce any veggies yet. You also need to avoid any sugary treats, including carrots. Just stick with the usual pellets and unlimited amounts of a good grass hay. In a couple weeks you may be ok to switch him to a new healthier pellet, making sure to do it gradually over a couple weeks, to give the buns digestive flora time to adapt to the new food. You just have to be very careful with young bunnies and changing their diets if they aren't currently having any digestive issues.

As for the urine, creamy colored urine can be a normal thing in rabbits, as excess calcium is excreted through the urine. However, if the urine is thick and sludgy, or your bun is dribbling urine, getting urine soaked fur despite keeping a clean litter box/cage, and/or the bun is showing any signs of discomfort, straining to urinate, or lack of appetite, this can be a signal of a potential health problem like a UTI or cystitis, and your bun needs to be seen by a vet right away.

His litter box and cage are cleaned frequently and his appetite is fine, is it still worth taking him to the vet or should I just keep a close eye on his behaviour and his pee for now and see how he goes.
And thank you for the information, I won't change his diet right away but I will adjust it gradually and take away the veggies.

Thanks for you help everyone.
Your advice prompted me to take him to the vet.
The poor little guys has a parasite (the name I coudl my pronounce not remember) it starts with the letter C anyhow...
They said it's a good thing I took him when I did or it might have gotten too bad!
He's on antibiotics for a week

Probably coccidia. Poor little one. I hope he starts feeling better!

Yes! That's the one.
I'm keeping a close eye on him and so far he is eating and drinking well, and he seems to be very happy!

I hope the little bun is feeling alright and the messy bum has cleared up. I'm glad you got him to your vet right away as coccidiosis is very serious and can be dangerous for little bunnies if left untreated. I don't know if your vet mentioned anything about disinfecting things, but cocci can be contagious through infected feces, so your other bun could be at risk, as well as a risk of recontamination for the bunny that was unwell. If your vet didn't discuss this with you, it would be good to give them a call and ask about it.

He seems to be fine now.
But no, the vet didn't mention this at all. Once he started medication everything was thoroughly cleaned before he went back to his little home, and my other bunny lives separately from him as they don't like each other at all.
How far do you have to go with disinfecting things? Is it more than just thoroughly cleaning his living space?

Ps.
He still had a messy bum.
Should I be concerned that the antibiotics haven't cleared it up? Aside from that he appears healthy, but I have had to clean him a few times.