HCG after D&C

I had an D&C December 30th. I didn't get my HCG tested until about 6-7 weeks after. My levels still haven't dropped. Has anyone experienced this? I was checked and everything is clear. And I have gotten my period twice since Dec 30th. The doctor just says its dropping slowly and it's not a problem. But didn't think I should try until it's a 0. It's torture waiting for this number to drop. 
Feb 15th: HCG 15
Feb 19th: HCG 11
Feb 27th: HCG 10
March 6th: 8
March 12th: 6
March 19th: 4