Ice and Advil...

"I don't ride hard and I don't stretch before or after I ride. "

While your muscles and lungs may not think they're pushing it, your knees think otherwise. Might be a good idea to do some stretching before and after. Make sure your heels can't touch the pedals when they're at the bottom and push on the pedals with your toes, not the ball of your foot or your heels.