hcg levels

Mariah • Iansmama
I had my hcg checked twice in 48 hrs. The first time it was 242. The second time it was 543. The nurse called me today and told me that the numbers are low. She said but they doubled. I have an ultrasound scheduled for this Thursday. Should I be worried because the numbers are so low? I am 5 weeks. I will be 6 weeks on Thursday.