Originally Posted by
Hitman
I think my seat height is ok, my legs are slightly bent at the bottom of the pedal stroke. I don't think I was in a hard gear, I was never out of breath at any point during the ride. I think it's time to go to the shop and check the fit of the bike.
I've always found improper bike fit would cause more back/shoulder pain, not knees. If you're sure of the seat and gear choices, then, as Bster13 said, it might be time to go get checked out by a doctor.