Low Progesterone & HCG not doubling- expect miscarriage?

I've been reading through so many forums, thought I might as well throw my case out there and hope for feedback.

1st pregnancy, first month trying. About 4 days after the positive hpt, (about 5 weeks) I had strong cramping and brown/reddish spotting and thought I may have miscarried, so went in for tests

1st on 12/14
hcg- 513
progesterone 5.2

Progesterone very low so was put on oral supplement 2 times a day

2nd on 12/16
hcg- 653
no prog. tested

Cramping has gone away but still brownish spotting, don't have many pregnancy symptoms- frequent urination, fatigued. All my nurse said was that we'll have to wait and see. But can't see anything on ultrasound until it is at 1,000 hcg. My question: if hcg continues to rise, is there any concern over the development of child?
I don't want to continue on progesterone and force anything if it's not meant to be. I wish I knew the percentage of miscarriage for this scenario.

If miscarriage, what should I expect? Does Dr. recommend it? After how many tests? I feel completely in the dark on this...I'm going to see my doctor tomorrow bit would love to hear personal experience (only been working through a non-respondent nurse as of now)

Thanks

[AnnieBrooke]

Progesterone will not force anything that is not meant to be.  The embryo will either continue to develop or it won't, progesterone is not a magic panacea that makes an embryo keep living that is otherwise not able to continue.  If you are miscarrying, it will fade whether or not your body has a period (which is the function of the progesterone -- it keeps you from losing your uterine lining).  They won't be able to see anything on ultrasound until your fifth week (if lucky) and your sixth week for sure, it's not about the hCG reading.  (A person might get high readings but only be a couple of weeks after conception, and it still wouldn't show up on an ultrasound.  The embryo is just too small at the early stages no matter what your hCG reading.  The concern here is the rate of rise of your hCG.  Are you going to have another hCG test?  I'd ask for one, since it is what tells you anything this early, not the ultrasound.

Anyway, don't be afraid to take the progesterone until you get an answer as to whether the embryo is with you or faded.  It won't hurt anything.  

Good luck!