If the antibiotic cleared it up a bit over a 7 day course, it's best to do a full 14 day course of the same antibiotic. The fact that the bacteria were killed by the antibiotic at least a little means they are sensitive to it. You need to kill them all by doing the full treatment course because if you switch to a different antibiotic now, the ones that remain will gain resistance to the original antibiotic. Does this make sense?
What I'm trying to say is that the bacteria that are still around are not as sensitive to the antibiotic as the ones that were killed were. If you continue to give the antibiotic, the remaining bacteria will get dosed with enough antibiotic to finally finish them off. If you switch to a different antibiotic now, the ones that remain will have adapted to survive the original antibiotic.