Suggest Treatment For Continuous Vaginal Spotting

I am a 19 year old women, have been spotting for 12 weeks and sometimes its heavy. I have had sever pain while urinating and have gone to the doc and they said i had a slight kind of bactiera but symtoms have come back 3 more times after. Sever pain, bloating Hurts to have sex, feel swollen inside of vagina. been texted for all std's all negitive. What could be wrong?