Six week doctor visit

I went in today for my six week postpartum visit and saw my regular doctor. She was on maternity leave when I delivered and just recently came back so she missed all the "excitement" I went through after having Jett. I filled her in on everything that happened and she wanted to do a sonogram and recheck my blood to make sure everything was back to normal. I really have been feeling fine so I expected the results to say so. After my sonogram she pulled me back into her office and informed me that my uterus is full again and under normal circumstances I would be going in for a D&C but since this would be my THIRD in a month she wants to try something else first. She put me on progesterone and wants me to try this first, basically she said it is a chemical D&C. I go back again in four weeks for another follow up visit, if things aren't cleared up by then I'll have to go in for another D&C. I asked her WHY this happened and what is causing it but she couldn't give me an answer, she said she has never seen this and has never seen someone that has required 2-3 D&C procedures. I'm frustrated and quite honestly scared.