hi, Well, you risk pregnancy every time you have unprotected sex. Sometimes we ovulate out of whack and we get an negative test because we tested earlier than we thought we should. But I doubt you are pregnant. Antibiotics and not feeling well can delay a period. That's common. Periods are often late when we are sick, worried, stressed, gained weight or lose weight, have a change in routine, etc. Brown spotting is old blood. So, wait week and take a test but just think your body is being off and acting weird and will soon get on track again. good luck
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