Sheree,
I am no expert but my understanding is that for the first 12 weeks, until the placenta takes over there is no big rise in progesterone levels and I think progesterone levels fluctuate throughout the day so that change may mean nothing. Your HCG is the main thing they look at and yours is rising well.
I am not saying this to worry you but - I have a box of progesterone pessaries in my cupboard, which I will not be using. i could send them to you if that would help ease your worrying. Apparently you can't give yourself too much progesterone.