Prolonged periods and irregular flow.

I have irregular period problem due to hormonal imbalance( confirmed by doc 2 years back). I am on heavier side of weight. Doctor said i should reduce weight. I couldnt reduce. 6 months back one yoga trainer said to take raw aloe vera gel for 45 days to regularize periods. I did so...i got my periods regularly after that...but periods are prolonged for 3 weeks every month. Not heavy flow but they come for 3 weeks. Starting with very very light flow initially( spotting) for a week or two weeks, then flow will start lasts upto 20 to 25 days totally. Previously i used to get menstrual cramps but that is not there now. Before this spotting start I feel severe back pain. Im 31 years old, married and have 7 year old0 child. Once bleeding stops with in a month I could get my periods back according to cycle but why is it prolonging for 20 to 25 days.....What might be reason behind?