Can antibiotic’s cause shorter period?

Mother’s Day 5/14 had protected sex with husband. He didn’t finish in condom and condom didn’t break. 2 days later I wasn’t sure if I was having UTI symptoms because I’ve never had one. Didn’t go the the doctors until 5/22 and turned out I had one. Started me on antibiotics for infection. 5/25 my “period” starts but was very light and lasted for maybe 3.5 days and normally mine periods are 5 days. After my period, I decided to take multiple pregnancy tests all came back negative. Today I noticed I had small amount of brownish blood like my period is going to start again. My question is could the stress from my UTI and antibiotics could have thrown off my period or could I be pregnant? I took another test today and was negative.