Cat has UTI

I took my cat to the vet last week, because I suspected a UTI. Sure enough he had one but she said he wasn't blocked. The vet gave him a shot and also some pills. I think I have four days left on the pill. He is less agitated, but today he was in the litter box and still only went a small amount. Do I wait until he's done with the antibiotic before I call the vets back?

IMO, it never hurts to just call and leave a message for your vet to call you back, or to speak with one of the vet techs...they can advise if they want you to wait until the entire course of antibiotics is over before taking your cat in for a re-check.