What is wrong with me? Abdominal pain issues?

Every few months, i get excruciating pain in my stomach. I cant really tell if its the stomach, or possibly the pancreas/gallbladder... this has been going on for a few years now. Except for once, this has generally happened in the middle of the night. i wake up and i am in a lot of pain, my stomach area feels like its a hard rock, i get really clammy and the only thing i can do to forget about the pain is go in the shower and lay there in the hot water to sleep. like i said, only happens every few months, so i am wondering what it could be. its not because i don't eat dinner, because i did eat dinner last night, not too late either. any ideas?