Low Progesterone and age

This past summer I was spotting at 6 weeks and when I went in for an ultra sound the baby's heart was beating and everything looked ok except it was a little smaller than it should have been.  The Dr. told me to have pelvic rest for two weeks and come back for another ultrasound.  The spotting stopped and I was getting very happy.  I was 38 and had two children previously without any problem whatsoever-no spotting-nothing.  I waited 5 years to go for the third baby and it seems everything was different.  I was having to take all these tests and it seemed so much more complicated.  Anyway, miscarriage never crossed my mind.  With the bleeding stopped, I thought I was out of the woods.  At the next ultrasound, the baby had made two weeks growth, which I was watching for, but then there was no heartbeat.  I was devastated.  I know it is common for women, but I just couldn't believe it.  Meanwhile the clock is ticking on my age.  I had D&C and waited two months.  I immediately got pregnant again and symptoms were present and it seemed even better than the last time.  But at 7 weeks, I started spotting.  My heart just sank.  I went to the doctors this last Monday, and baby was there with good heartbeat and all.  I was more concerned this time, suggesting there must be something with my hormones. You know you can feel what is happening to your body.  You have a certain intuition. It is like everything starts out fine and then at about 6-7 weeks my body stops doing something.  I asked about progesterone, not completely aware about its relevance, and the Dr. drew blood.  My progesterone was 8.3.  The Dr. said that it was normal, but everything I read suggests differently.  She put me on 100 mg supplements 2 times a day.  I kid you not, I stopped bleeding two hours later and haven't bled since.  My uterus is beginning to feel fuller and then it came to me that maybe my last pregnancy failed because of the same thing.  I asked Dr. but they said the levels were normal, they also said these levels were normal.  I went in to days later to do a repeat hcg test.  On Monday it was 5,700, and on Wednesday is only went up to 6,300.  When I called for the results the lab said it didn't look good.  My heart just sank.  I thought maybe it just isn't meant to be for me.  I felt that the concerns about progesterone are correct.  Levels are low because the body is going to miscarry and so it drops.  The Dr. wanted a repeat hcg yesterday, Friday, and a sonogram for Monday.  I left work early to do it because I wanted the results the same day-no way I was going to suffer through this weekend wondering what was the verdict.  I did not go with any hopes.  I was expecting it to rise only 100 more than Wedneday, or worse drop.  When I called later in the afternoon, it had gone from 6,300-9,800!!!!  It had risen!! Now I am thinking the progesterone is kicking in.  I had only been on it 4 days.  Maybe Wednesday it just had no effect.  I am now more optimistic.  Could this be a progesterone problem?  I will do a repeat hcg and progesterone test on Monday and a sonogram.  I will let you know how things go.  I pray this is the problem and that my hcgs really rise.  I also pray that the baby is ok.  I hope that during this period of lack of prog. there aren't defects or problems with my baby.
I would LOVE to know if others have been in this situation.  I hear so many contrary things.  I just need hope.  I want this baby more than anything.  I want it healthy and thriving.