Hcg levels

Kierstin

I’m pregnant but not sure how far maybe 3 to 5 weeks. I went to check my hcg levels 42 was the first one then two days later it was 120.. one week later and it’s 1,619. The doctor wants to check again In another week from now to see the levels. How far along am I? And why can’t I get an ultra sound now? Are My hcg not high enough?