I'm very sorry about your loss. So disappointing after all that you have been through already.
The type of checking your gyn was doing is quite normal though with your type of situation. If a pg occurs, they will monitor it very carefully at first with scans. They also do blood tests as you described to check whether the hcG levels are still rising which will indicate viability.
I know it doesn't help much at the moment because you will be thinking about the one you have just lost but falling pg so quickly after the lap is a very good sign. It means the lap did the job and I hope it isn't too long before you conceive again.
Once again, I'm really sorry. Rest up and take care of yourself.
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