Hi, i am a 19 year old female not on birth control, and i have missed my period by 4 days now. the last intercourse i had was precisely 4 weeks ago with my boyfriend, and right when my app predicted my ovulation (around 3 weeks ago) i got diagnosed with a kidney infection and was on amoxicilin (antibiotics) for 10 days and also heavy painkillers. now that my period is late i am having all the symptoms i normally have before my period, and i got very stressed so i took two pregnancy tests on the third day that my period was late and they were both negative. is it possible that the stress and the use of medicine threw off my cycle? the sex was unprotected but i am 100% sure that there was no ejaculation inside, i just want to know if its normal that my period is late and what the cause could be. would be very helpful if i got answers, my mind keeps going to those tests wondering if they're false negatives! thank you :)