Sounds like you need to contact your doctor because it could be acid reflux, pnuemonia or even blood clots. About two weeks after my surgery i started feeling pain in my upper stomach and back on the left side that would not go away. I contacted my doctor he had me come in for a CT-Scan and found that I had blood clots in my stomach. So please don't take any chances with this go and have it checked out. Good luck!