What Cases Irregular Periods After Delivery Of Child?

hi. I am 27 years old. I had my delivery in august 2010. It was a normal delivery. I am wearing a loop since january 2011. I got my periods after delivery from feb 24, 2011. The next one came in 20 days and the one in april came after 28 days but lasted for 2 weeks. not a very heavy flow but brownish lumps. The one in may also was same like april. Is it normal to have like this? also I feel pain in the vaginal area after intercourse. Also have bleeding sometimes. It is also swollen sometimes.