What could cause me to bleed for months?

I had gotten an abortion in April because I was in an unhealthy relationship, i Ik have 2 older sons, but furthermore I am still bleeding lightly. I also am on Depo and am due for my next shot this month. The doctor said that this is normal and my body is getting used to the birth-control but I’ve been on this birth control before and I have not bleed for 3 months straight. I would really like to go swimming and not be wearing diapers anymore… What are your thoughts on this?.