Chances of miscarriage

So what are the chances of having a miscarriage now? Just worried because I've previously had a missed miscarriage (was supposed to be 11 weeks but baby stopped developing at 8) as well as a chemical. I'm 10 weeks 5 days and we had an ultrasound done at 6 weeks 6 days and everything looked healthy. I bought a doppler and was able to find the heartbeat for 2 days in a row and then wasn't able to find it for a day and then found it but only very briefly and now I can't find it again.