My doctor ok'd riding too but said watch heat and keep heartrate under 140!
I finally had to stop riding at 7 months, too, because of the knee/belly thing. I kept hiking up to the end, though, and used my DH's heartrate monitor.

Maybe it had an effect on the little guy-he LOVES bike riding and will sit in a trailer for HOURS without complaint.
I'm lucky lucky lucky lucky lucky lucky!!!!!

Best of luck with your pregnancy, here's to all going well!