Brown discharge after sex

Patient: I’m a 16 year old girl, and my boyfriend and i recently made the decision to have sex. We had condoms, but today we didn’t have any around. We decided to do it without a condom, but it was only for about 30 seconds and i made him stop before he ejaculated. My day after that was pretty normal. But when i went to go to the restroom, i noticed a brown discharge in my underwear. It really caught me by a surprise. I didn’t have brown discharge the few other times we had sex.

Symptoms: Brown discharge, mild cramps