Hi Xeney
i had problems walking in my third trimester too, (of 1st pregnancy) my hips were loose and oh it hurt so badly... and then i'd get cramps from walking.
I had my kids right after they discovered that limiting moms to 20 pounds of weight gain was stupid, so I gained almost 40 pounds with each kid and no one dared to tell me anything about that weight gain. I lost it all too, within 4 months. Breast feeding helps with that.

I didn't ride bikes back then, but I did ride horses. After I started showing I just slowed down and quit riding. Some of the gals on here do amazing things while pregnant, but your doctor's advice sounds excellent good luck!