How long after a loss?

[LysnDan]

How long after a loss (at 4w6d) does a positive test go away?

I've had my bhcg drawn on Friday and it was 12. That night, I ended up at the hospital with sharp pains and spotting. Today I have had quite heavy red blood (slightly worse than a period) but positive tests on both a frer and a clearblue digital???

What the heck is going on? :-(

It's so confusing. I just want to know either way. They were adamant I was miscarrying at the hospital on Friday night given the amount of pain I'm in. They gave me an anti d shot too.

I have another blood test for bhcg tomorrow (and get the result tomorrow afternoon) but I'm just so confused as I was told my beta was way too low for a continuing pregnancy given my dates. :-(