HCG levels

I had a D&C on December 30th. My levels weren't tested until recently. I had my period four weeks after the D&C. My HCG level was 15 last week, 11 today (7 weeks after D&C). Is it normal to have had a period without the HCG level being 0? I monitored my LH levels after I got my period, which was heavier and longer than usual, it was negative for a few days last week, got a little darker as the week went on and surged on Saturday. I just didn't think any of this would go on until my HCG level was 0.