Antibiotics setting off period

About 4 nd a half weeks ago I had sex with my boyfriend and it was unprotected. I was on my period at the time (just about ending it) and he didn't ejaculate inside of me but a few days later I got a uti from not peeing after sex. Anyways, I got put on antibiotics that made me have no appetite and I lost quite a bit of weight. I was supposed to have gotten my period 4 days ago and I'm worried. I know there's an extremely small chance I'm pregnant but could the antibiotics have set off my period?