progesterone and miscarriage

Hi ladies- I have been on progesterone to maintain pregnancy for the last 10 weeks. (I had to take progesterone for the first 14 weeks with my son) I have had several ultrasounds because at first they were thinking my dates were just off-- I had an US almost 2 weeks ago and baby was measuring 6w 5days with a heartbeat. I had another ultrasound on Monday and should have been around 8 weeks and maybe was now measuring 6w 1d and there was no heartbeat. I stopped my progesterone on Monday and am hoping to miscarry naturally. I was wondering if anyone has miscarried after being on progesterone and how long it took after you stopped the progesterone to start to miscarry? I just don't know what to expect and the waiting is so hard.