K.N.
Low HCG can indicate issues like and ectopic which someone mentioned, but can also just vary greatly person to person and is more an issue of it the numbers go up (they should double about every other day). After a couple blood tests to determine if your HCG levels are going up, if they are still concerned your doc should do an ultrasound.
Low progesterone is actually a bigger deal, but you caught it really early, and your doc seems to be on the ball in treating the issue. The next step if your current medication doesn't work would be injections.
I've had two miscarriages in the past year (and am thankfully 36 weeks pregnant) and while low progesterone can cause a loss, it's easy to treat and doesn't indicate that anything is or would actually be wrong with the baby.
good luck.