What Causes Intense Burning Sensation In Uterus Along With Prolonged Periods?

I get a intense burning through my uterus and my periods last up to 2 weeks and i have to use a pad and tampon and i still bleed down my legs. I had seen a doctor they did a pap and everything came back normal they said i had some scar tissue. Last year i had a positive pregancy test 2 weeks after i had intense sharp pains and started to bleed alot. The scar tissue was seen by a doctor after this situation. I get a period twice a month at times or ill go from the begining of one month and wont have a period until the end of the next month or begining of the following month as well. My menstral cycle is all over the place.