Second beta/progesterone result

In the ongoing saga of actually getting my blood test results, which involved about 5 phone calls, a voicemail this morning, and eventually my lovely husband calling this afternoon because I was so frustrated and getting nowhere - three long days of waiting, and the results are both good and bad:

HCG = 5468 (up from 620 a week earlier; a doubling time of about 52 hours, I think)

Progesterone = 7.8 (down from 15.3 a week earlier)

I'm not happy with my progesterone level at all, so I called back and left a message for my OB to call me back. She called within a couple of minutes, and told me that she thinks my progesterone is fine. I know I'm not a doctor, but everything I've read states that progesterone should be at least 15. The fact that it dropped by about 50% in one week really worries me. I told her that it's taken us so long to get pregnant and I'm really concerned that my progesterone levels aren't high enough. I really don't want to lose this baby if we can prevent it! She offered to put me on a progesterone supplement, which I gladly accepted. I know she probably thinks I'm a giant pain in the ass, but at least I'll know I'm doing everything within my power to keep our little one safe. She said my HCG level is great, but I know that's not the whole story. Progesterone is needed to sustain the pregnancy until the placenta takes over, and I don't want it to be low and do nothing about it! She told me she doesn't usually test for progesterone, but my reasoning is that she did test for it (twice) and a low level shouldn't be ignored.

Anyway, she told me she'd call my prescription in to my local pharmacy right away. We left home about 20 minutes later, and when we got there they had nothing. Great... I'll have to call them soon to see if they have it yet. Hopefully they will before they close tonight!