What could be causing this pain in the middle, right-side of my abdomen?

Dear Ask The Doctor: I've been experiencing pain in the middle of my abdomen, on the right hand side. It's not excruciating or sharp; it's more like a dull ache. It almost feels as though someone is slowly pressing a blunt object into my stomach. It has been coming and going, on and off, for a couple of months now, sometimes with a few weeks passing without experiencing any pain at all. I went to see my GP, who said that my gallbladder is situated where I am experiencing the pain. I was referred for a scan of my gallbladder, but the results were normal. It does not seem to be food related (i.e. it does not worsen after a meal). I'm not overweight, and I don't smoke, and rarely drink alcohol. I have noticed, however, that when I have the pain, I seem to feel bloated too, and I do experience feeling bloated quite frequently. What else, besides gallstones, can cause this type of pain in this area? Thank you.

Dear Cheryl: Other cause that could cause similar symptoms could be reflux disease, gastritis, gastric or duodenal ulcer and pancreatitis. An upper GI endoscopy, test for H.pylori and serum lipase may be required to make a definitive diagnosis.