Recurrent Bladder Infections. Painful, Burning Urination. Cause?

About a year ago I started to get bladder infections. I went to the doctors and had different tests done, but no one could work out what it was and it went away on its own so I stopped going to the doctors. Its been about four or five months since I ve last had an infection but I got one right now and its incredibly painful. It burns when I pee, but burns alot more just after I finish and for a while after. Nothing I do seems to be helping. Alot of things have changed recently so I can t pinpoint exactly what it is, I ve started having intercourse with my boyfriend, though with pervious partners I ve never had problems. Its started to get colder here so I don t know if that s the cause either, and I ve gone back to school so maybe stressed? I dont know I just know im in alot of pain and need something to do about it. Please help... Emily. YYYY@YYYY