Congratulations! Sounds like your little guy is growing almost as fast as my son did. He was 8.7 at birth and gained 2 lbs by his 1 week checkup!
It's hard to remember when I started working out after my first pregnancy as that was 6 1/2 years ago. I would imagine that I waited the whole 6 weeks, unless I was walking. I was pretty new to working out back then and would have been taking things much slower. With my daughter, I started at 2 weeks postpartum. I eased back into things slowly, and by 3-4 weeks, was doing the Cross Train Express Series (Brand new out at the time). The bleeding did pick up a little but not a lot when I started working out.
Hope that helps!