Sick Kitten...How long does it take for medicine to start working?

I have a kitten that I took to the vet a week ago. They told me he has an upper respiratory infection and prescribed an antibiotic and some ointment for his eyes. It has been a week now that I have been giving him his meds and he is a little better but is still sneezing and has the crusty, runny eyes (not as bad as a week ago though). How long does it take for medicine to take affect? Should he be better by now? Is there another illness that he may have besides an upper respiratory infection that would have the same symptoms as a URI?