drop in levels

Has anyone had a slight drop in their hcg levels? I am 10 weeks and have been experiencing some slight spotting, but no cramps. We checked my hormone levels and my progesterone is more than double what it needs to be but my hcg levels have dropped slightly. My dr isn't too concerned because we were able to hear the heartbeat and my ultrasound a week ago was good and didn't show any hemorrhages. They said we will probably recheck next week but isn't too concerned with it because he said that sometimes it does happen and my progesterone is good. 

Has anyone else had this happen?

This is my 9 week ultrasound.