That situation is identical to what I went through when I miscarried in Jan. By the time I went to the ER (because my Dr's at that time were morons) my levels were at only 14 and I was at about 6 weeks. Never once did they try and tell me how far along they thought I was. They did do a few ultra sounds to see if they could find a sac (which they didnt). Maybe they were saying that so it didnt seem like such a loss, which we all know thats not true. Well best wishes, I hope all works out.
Bleeding can be normal during pregnancy or it could be a sign of a miscarriage. I'm surprised that they told you the week you would be based on your levels since it can differ greatly from person to person. Its not really the level that matters but whether or not it is doubling in the 72 hour time frame. The only thing I can really say is wait for the next results since they should be able to give you more information about what is going on. Best of luck to you I hope everything works out okay.
Unfortunately it may be possible that you miscarried.....Your would have still had a + HPT on Monday, as it can take days to weeks after a M/C for your levels to drop......Of course, I may be wrong, that's just what it sounds like to me....Others may have more insight.....Best wished and please keep us all posted.