I'm not sure if I am having an Early Miscarriage??

I have a pretty regular cycle and always mark down when I get my period so I know my ovulation cycle... Except in January when we moved into our first home and everything was plain hectic! At some point between December and January I fell pregnant with our second baby. I can not remember having a period in January (but don't know if it is because I actually missed it or if it was just so busy I've forgotten about it). I estimate that I am somewhere between 6-10 weeks pregnant.Anyway, on Tuesday I had a small bleed which I assumed to be an implantation bleed. I wasn't too concerned because I bled all the way through my first pregnancy, quite heavily, and I had a very big and very healthy little girl in the end. So I did what I did for every bleed during my first pregnancy, I had a cup of tea and went to bed for a sleep. When I got up there was no more bleeding.

The next morning at approx 4am I went to the toilet where I had a heavy bleed. I went to my doctor at about 930am who ordered an ultrasound to determine what was going on as well as determine how far along in the pregnancy I was. By lunch time I was still having heavy bleeding and felt lots of menstrual pain. I called the hospital to discuss my symptoms and they advised I go straight to emergency which I did. I had some blood tests and after much waiting around the results said that my HCG levels were low around 950ish and the doctor said that if I was around 6 weeks pregnant I should have a reading of 1200+. I accepted that I was in the process of an early miscarriage and went home with my young family and had a little cry with my husband.

I went to the ultrasound yesterday where the women measured my yolk sac to be approx. 5 weeks in gestation but that there didn't seem to be a fetus in the egg. This somehow made me feel better, I don't know why, it just did.Today I went to my GP for another follow up and he said that the yolk sac was too small to determine whether there was anything alive in there. He made me do another urine HCG test which again returned a positive pregnancy result. He has also ordered another HCG blood test to monitor my levels (he said that if they continue to fall that I am in the process of having an early miscarriage). My problem is is that I accepted and have been grieving the lost pregnancy with my husband and now the doctor has put doubt in my head and I don't know what to think. I would like to know if anyone else has experienced heavy bleeding with clotting and cramps during their pregnancy and whether there was a reasonable explanation for their bleed. I have now had heavy bleeding for 4 days, like I have never had before and really would like to know if this has happened to anyone else. Help please.