Hi, My Boyfriend Has Severe Pain While Urinating. He Went

hi,
my boyfriend has severe pain while urinating. He went to two different doctors and they both did a culture which both came back negative. At the hospital they gave him a CAT scan and said everything appeared healthy. He has been put on three different antibiotics. Two strong ones (incase it was an STD) and then a script for ten days. At the hospital they gave him a large shot in the butt and sent him home with the instruction to keep taking the other antibiotics. This was two nights ago. Five days ago he started the antibiotics and it is getting worse......What is going on?