Hi!
It appears unlikely that Mr. Rebound is the man. With a due date of 9/28/2010 your conception date should be Jan 6. There is up to a two week error in an ultrasound, so it could have been even two weeks earlier than that, but even so, that puts your conception date no earlier than Dec 23, which is still a week after Mr. R.
I think BF is probably the dad. A DNA test is the way to know with 100% certainty. They typically cost around $1000. If it would make a difference in what happens next,
You might want to think about having one done. Your Ob doctor should know how to do it.
Good luck!
Dr B
If the dates are correct it looks like you could have conceived from the 6th to the 11th and should most definately be your old boyfriends baby not your rebound.. Hope this helps.