30minutes after eating way too much for lunch because i was very hungry,i started feeling a pain in stomach radiating to the back.i have very frequent belching and feel like a lot of gas is in my stomach.can gas in stomach cause upper back pain?

Your symptoms may not necessarily be due to gas itself, but may be due to being overly full and perhaps having acid reflux. You may want to take a short trial of acid reducing medication for one to two weeks to see if it helps. If it does not, you should make an appointment to see your doctor or a gastroenterologist if the symptoms are persisting. Good luck.