Possible miscarriage?

Alyssa • A Corrections Officer and Dispatcher, I am happily with my fiance, soon to be husband. We miscarried November 5th, 2015 with our 1st, I am pregnant...again! Hoping this one makes it. I'm very excited!
Just found out I am pregnant, not even sure how far along I am. I'm thinking around 3-4 weeks. Today I started my period, like started out heavy and although it's still not as heavy, it's consistant. I have cramping and uncomfortable lower back pain. I called the OB triage nurse and she wanted me in for a blood test. I'm happy that I am not rH-, but I am O+, so luckily I do not need injections. But, my pregnancy hormone is at level 3. She says she is very concerned about how low it is, but I feel like it's going to be okay, but still worried. I've never been pregnant before, does anyone have advice for me? I'm so scared that I'm going to miscarry. I go back for another blood draw on saturday to see if my levels go up.