My first pregnancy I had spotting til my 12th week. I told the OB and he said not to worry, it's normal. But, if it becomes heavier to call back.
Since you've taken HCG levels and they're looking good, I would try to relax. I know, better said than done.
You may want to ask the nurse or the doctor, if it may be because of progesterone level. I don't know, just a thought.
I just found out yesterday of my BFP and I don't feel any inkling of any pg symptoms. I think I felt more sypmtoms before the BFP.