Burning

Okay, so my boyfriend and I had sex for the first time about 3 weeks ago. I had just gotten off my period(like the day before) and we were very careful(with condom and cleanliness). But for about 2 weeks my pee burns. The first week(week after sex) I went to the doctor to check for a UTI and it was negative, although there was blood in my urine. She said it was most likely bladder spasms. She suggested AZO and then about 5 days later after my symptoms were still about the same she suggested I come in again for another test, which also turned out negative. That was 6 days ago and I thought I was better but today I woke up and the burning is so bad! I just had to walk out of work because I started crying(I last peed about 10 mins ago and it's still stinging). I know things tear down there sometimes, but is it normal to have lasted this long? Has anyone else had a similar experience? I need advice!