I Have Been Having Very Heavy Menstrual Cycles. I Can

I have been having very heavy menstrual cycles. I can go through a box of tampons in a day. I soil my sheets and clothes with blood. It has gotten so bad I have to sleep with towels under me for those days. This last period was really bad. I went to the doctor because of the excessive blood loss and cramps but also my upper abdomen is hard and distended. I know bloating happens during a woman's menstrual cycle. But my period is done and the distended abdomen isn't going away. I can barely eat. All my blood tests at the doctor came back normal except my iron levels were 5%. I was prescribed iron to take. Right now all my bowels are moving okay. I am barely eating but I am so afraid of taking iron with my distended abdomen because the last thing I need on top of everything else is to get constipated. The last time I was constipated I took an over the counter laxative and it lowered my potassium levels dangerously low. So I am trying to stay regular so I don't have to go through that again. Could it be fibroids pushing on other organs, could it be a thick uterus? Could they be completely unrelated? Could it be celiac disease? But this abdominal issue didn't start until I had my period.