progesterone levels dropped at nine weeks

OB called this morning and told me my progesterone levels are very low and they are putting me on supplements. Crinone is the medication the called in... When I was eeeing my RE still at 6 weeks the levels were 21, which the RE said was great. I dont understand how they went down and I dont understand why it took a week to get this info to me! So now Im scared to death because I already had a miscarriage and if I lose this little one I will lose my mind.