Hcg levels?

Hey every one. We just got our BFP last week and I went to the Dr. 2 days ago for an hcg. On Monday it was 239 and today Wednesday it was at about 400. Are these numbers normal? Today I am cycle day 33 and I have an 8 year old and a 2 year old. I never did this test before but they did it this time because my last pregnancy was a miscarriage at 8 weeks. What is a normal number supposed to be? Any help as to if I should keep testing this or wait until my ultrasound next Friday ?