Losing It...miscarriage story.

I am really new to this but I have kept this all a secret from basically everyone I know so I come here for support and hopefully similar stories to give me hope. So I guess I will start off with my story and what's going on with me currently. I will date this back to about the time I could really tell I was pregnant. This was about a week before my period was to start. I could tell I was pregnant so about a week after af was due I took a test and it came back quickly positive. Literally three days later I start to spot. I panicked and called a doctor to try to get in. (I feared that it was ectopic) Once I was seen everything looked great. Nothing could be seen, but remember this was extremely early. I can't remember what my hcg was at anymore but it was tested 48 hours later and seemed to be doubling. Anyways, all seemed well and the doctor sent me on my way and told me to come back in a week since I was having the bleeding so we could do another ultrasound. Okay, second ultrasound looked great as well, but there was no heartbeat to be seen as it was still early. I had also stopped spotting at this point so I was feeling much better about everything. You could see the fetal pole and sac and it was measuring at 5.5 weeks I believe. I was told to come back in two weeks. Two weeks later I go in for ultrasound and they can not see a heartbeat. However now, there are two fetal poles (momo twins). Neither have heartbeats and one is measuring at 5.6 and the other at 6.1. By this point I am predicted to be at 8.5 weeks so the doctor is not very optimistic. She does blood work and asks me to come back in a week to make sure it has not grown for sure. My hcg was at 33,000 and she says my progesterone was around 4. My question is, how is it possible that my progesterone would be that low with my hcg still showing so high? I'm so confused with everything. I have now been spotting for almost two weeks with no signs of it increasing any soon. Why has my body not miscarried? Why have I just steadily spotted for so long?