Sorry you're going through this. My understanding is the hcg should be negative within 2-3 weeks after you've passed everything. I'm not there yet (I'm 10 weeks, but still waiting as I had a missed mc), but my midwife has told me to use a pregnancy test 3 weeks after the miscarriage itself (passing the sac, placenta, etc.) to confirm that hcg is negative. I'm assuming it's possible then to have some hcg up until then, depending especially on how far along you are and how high it was to begin with.
My understanding is also that the advice now is that you can try again right away and don't need to wait, depending of course on how you are feeling and whether you want to, though you should at least wait until the bleeding has stopped, which could last several weeks. We are planning to wait until mid-May sometime. We have an overseas trip planned for several weeks in the second half of May and I don't want to be newly pregnant again when we leave for that (I would have been in 2nd trimester by then, which is why we planned it like we did). So we plan to start again either when we're away or as soon as I ovulate after that, just to give me a little bit of time and get to enjoy our trip without being sick or stressing about a new pregnancy. But really as soon as the bleeding stops, if you are feeling up for it, there's no need to wait.
