Hcg levels...

I'm supposed to be 5w3d. This past friday my hcg levels were at 48... I had another check yesterday (4 days later) and they are 160. I go back tomorrow for another blood draw. This is my 4th pregnancy and my hcg levels were never this low. I'm kinda scared. Are they going up like they should? Maybe I ovulated later and I'm really only 2-3 weeks? I dont have an ultrasound until the 9th and see the dr on the 10th. I need some advice, prayers and positive vibes please!