I forgot, my Doctor told me to consider the first day of my miscarriage the day first day of my last period so...also I dont think your levels will go all the way back down if you miscarry 1 and are still carrying the other.
Yes it could just be that one time, I miscarried Feb 7th and got a BFP March 7th and I could just about tell you the day it happened....
The best thing to do is to call you dr. and make an appt. and then he will have to set you up with an u/s. And yes, it only takes once.....