low progesterone with happy ending?

Just wondering if anyone here has had problems with low progesterone and still carries to full term. My hcg levels are good but my progesterone was 7.7 at 5 weeks. I started oral supplements and I begin injections twice weekly next week (or whenever it arrives to my house!). What do you think? Are these levels too low or did I start the progesterone too late? I've had cramping but no spotting yet. Hoping for the best.