Antibiotics and period?!?

Hi ladies. I was on an antibiotic for uti from cd 14 of one cycle to cd 16 of next. It took 3 antibiotics to clear up. My period is due today but i only have brown spotting that started 2 days ago, its like my body knows its time but cant get in gear lol there is a tiny chance of pregnancy but im more concerned if the antibiotics is causing the whackiness. Can anybody help?? Thanks