Is there anyposiblity I could have Cancer. Please help!?

Hi. So I am teen. I have stomach problems. My pain is right between my rips in the center. Sometimes it gets so bad I can’t move. I can’t eat fatty foods or spices or sugar because it makes it worse. But ice-cream doesn’t hurt? I’m on an only water to drink diet and I guess it’s helping I am also on pain meds that rarely work. Sometimes I am in extreme pain and I fell like ping out. I also get major headaches all the time. I’ve seen a GI at children’s and they gave me a few possibilities to what could be wrong. They said I most like have intestine problems. Where my intestine doesn’t work right. They also said I may have allsore in my stomach. I’m going to have an operation where they put a camera on a tune and put it in my stomach. Do you think they’ll find anything? Could I have a tumor inside my stomach? I have a lump on my neck that’s new if that’s related to anything. What do you think is wrong with me? I’m confused and I just want to be fixed this has been going on for like 5 months. I have had my gall bladder looked at. It's fine.