Declining HCG levels

I have two beautiful boys, ages 5 and 3. I had a miscarriage 18 months ago. Since then my peroids have been really heavy and I am passing clots the size of quarters to golf balls. I also have painful cramps before and during my peroid. My doctor has tried numerous pain meds to help with the cramping but doesn't seem to be concerned about the clots and heavy flow.
Well now I am pregnant again and my doctor wants to monitor this pregnancy more closely. I am 5 weeks along. On 3/18 my progesterone was 16 and my HCG was 87. Today, 3/20, my HCG is 64. The nurses say that I will most likely miscarry again. I am supposed to repeat the HCG test on Monday the 24th. I am scared and want to know what is going on with my body. Why is this happening to me? I am 29 and should be able to have a normal pregancy just like my first two. Will I miscarry again based on my HCG results? Also, I do feel cramping but I have been really gassey the past week. Should this be a concern to having a miscarriage? If anyone has any help you could possibly prepare me for the worst or help me to pray fro the best. Thanks.

[W8NGONHIM]

I just wanted you to know that I had a miscarriage 8 weeks ago and I also have two boys, a 4 yr old and a 2 yr old---I will be praying for you and God's will for your family. Wait on Him....for He is faithful!
Praising Him!
Amanda