can someone explain why this is happening

hi

i’m on bc now and i’m sexually active

i last had sex on the fourth of july or maybe a few days after i don’t remember.

i got put on antibiotics due to an infection and i haven’t had sex since.

i’m not even close to my period. i’m right in the middle of my pack. i’ve been getting really bad “period” like cramping, no period.. my chest is also really sore and heavy. this never happens to me as im right in the middle of my pack and symptoms don’t usually start for me until i stop taking the active pills. i’m actually really confused as to why this is happening. can someone explain the possibilities? should i see a doctor?