What Causes Pain And Irritation In Penis After Having Intercourse?

Hello, a friend of mine had a one night stand and the condom broke at the tip. He found some possible mentrual blood on his penis and washed it off with soapy water. The next day he began taking 500mg of amoxicillin 3-4 times per day for 6-7 days as a precaution. About 3 days after possible exposure he developed a mild irritation in his penis shaft. He also had other mild symptoms which included sore throat in the morning, chills, joint pain in hand knuckles, feeling weak (hard to make a tight fist), chest pain around heart. He went to std clinic 2 weeks after exposure and they took blood and took penis swab. Found possible NGU and issued medication just in case. All initial tests including HIV were negative that day. Was told to follow up in a week to receive in depth lab results and all came back negative including HIV. However he is still feeling those mild symptoms with the exception of penis pain daily. Is it possible he contacted something the doctor didn t discover from the encounter or is this just a placebo effect?