I had a baby four months ago and i've had my period for almost 3 weeks with very heavy bleeding and very large blood clots including pelvic pain?

See your ob/gyn: First, make an appointment to have your ob/gyn take a full menstruation history and perform a pelvic exam and blood counts. You can start to take at least 200mg of Ibuprofen to help slow the bleeding and help with the pain, up to 4 tabs. It could be an excess of estrogen, possible pregnancy as well. There are Rx hormones that can stop the bleeding but you need an exam first to confirm no pregnancy