Slow rising HCG levels at around 8 wks...thoughts?

Some of you will know, from my other threads, that I am worrying about slow rising HCG levels that I have...my scan results are good, (have had two, one at just before 7 weeks, and one a week later) with a strong heart beat etc...and yet my OB keeps saying things could go either way as my HCG levels just aren't fitting the normal pattern and have slowed down, and are now rising bit by bit.
I assume lots of pregnancies don't fit the mould, but it's always encouraging to hear other positive stories from people who maybe didn't fit the mould either!
My levels have been 8,600 (6 weeks, 2 days)
a week later, 10,500
3 days later 11,600 ( that was last friday, when I was 7 weeks, 5 days)

I am thinking positive, and feel my little one is doing OK, but it's just the medical words of caution which do roll around my head a bit (until I tell them to go away and resume my positive thinking)