Recently while exercising like bike riding. my heart rate goes to 185 and pounds. i feel nausea and pain in my stomache. what could be wrong?

Exercising: You are approaching a theoretical maximum heart rate for you age. This in and of itself may cause your symptoms. Usually you would treat by slowing down to keep your heart rate at a more comfortable rate. Can have problems that involve the blood supply to the inferior portion or your heart that can give you the same symptoms. I would monitor this as you keep your heart rate less than 160.

Stay hydrated: It is possible that you are overdoing it, but many people your age can sustain a heart rate of 185. A likely culprit is dehydration which can cause both stomach pain and nausea. Alternating between water and powerade can be very helpful. Good luck.