Dear Cocoo,
Dropping HCG and low progesterone are not good signs at all. You can try progesterone supplement like Crinone - that can help prevent miscarriage due to hormonal insufficiency. But it cannot prevent a miscarriage that is due to genetic malady. This is the most common type of miscarriage and has happened to me twice. The bad news is that this one was a "dud", either the egg or the sperm was bad and not able to form a live baby. BUT the good news is that you CAN conceive, you CAN get pregnant which is HUGE....you cant imagine how huge until you've sat in the waiting room of an infertility doc. Genetic mistakes, bad eggs, bad sperms - they are quite common and although its very hard to hear this now, you WILL be able to conceive again in about 3 months if this one turns out not to be viable. Look at it as a "practice" pregnancy and that may help you get thru this most difficult time.
I wish you all the very best. And if it turns out that you have an "angel" (due to miscarriage) then the little angel will forever and always look out for the ones who live. God/Allah never gives more than you can bear...never forget that and you will endure.
Prayers to you.
Agree with Mo3.
May Allah bless you with a healthy baby.
Lean on your husband for support.