Just to update: I did another test yesterday, which was another weak positive. The clinic were very good and got me in for a blood test, which has shown low HCG. They said it could be that the embryo tried to implant but that it isn't continuing, so it's a very early missed miscarriage or a "chemical" as people on like to call them, but I think that makes it sound like it wasn't real! There was HCG in my system and it was being picked up by pregnancy tests, but it's not enough for a pregnancy to be continuing. This is a negative result, but at least I was more prepared for it than yesterday after getting a thin positive line. Christmas will be a nice distraction and then we have 1 more frozen embryo to go again with in the new year.
Merry Christmas! Thinking of all of you who are testing today or are testing over this period.