Hi OP. Sorry for your loss. Did you have a spontaneous miscarriage or a missed miscarriage? Have you had a scan to check your miscarriage is complete?
Unfortunately it can take a while for your HCG to return to zero after a miscarriage, and your OPKS will still show positive even with quite a small amount of HCG in your system. OPKs can't tell the difference between LH and HCG.
I'm not sure exactly how high your LH needs to be for the OPK to turn positive - higher than the level of HCG that turns a pregnancy test positive, but still less than 100 I think. After my previous miscarriages it has taken a couple of weeks for my HCG to get from the low 100s back to zero, even when the initial fall from the much higher numbers was much quicker.
For this reason I wouldn't start trying to use OPKs again until you get a completely negative pregnancy test.
It is possible to ovulate with a low amount of HCG still in your system after a miscarriage. I'm pretty sure this happened to me at least twice. If this happens to you and you have been trying in the meantime then you will not necessarily know when you ovulated or when to test. If you think this is likely to stress you out then the simplest solution is to wait for your first period and then start trying again and tracking your ovulation after that. If you don't want to wait for your period, then just keep trying, and if you haven't had your period by four weeks from the date of your negative pregnancy test, do a test. If it's negative, wait another week to see if you get your period, and if you don't, test again.
I recommend buying a box of cheap strip tests from Amazon to track your HCG back to zero. The easy@home ones are very sensitive.