Sometimes about 20 minutes after eatingI have severe abdominal pain followed by nausea, chills, and back pain.

You may have Gal-stones. That sounds very similar to the symptoms I had. I had to have my gal-bladder removed. Talk to your doctor.

this sounds like its most likely from acid buildup or bloating or gas. try just not to eat as fast and if it still occurs sea your doctor.

Try changeing what and when you eat.

Or try eating less more often.

I have had very similar problems to you with unbearable sharp pains in my abdomin after eating. My solution would be to eat more slowly and make a record of what you have just eaten before you get the pains. Some examples of what I must now avoid are acidy foods/drinks (eg. oranges). With your record, you should to see the doctors and they may be able to help you as they have done with me.

I had that exact same problem you have, after I would eat (about an hour would pass) I'd get really harsh pain in my upper abdomin and my back, my pain went on for about a year until doctors found out what was wrong. I had gallstones, they're a build up of acid or calcium etc in your gallbladder, the pain is caused when a stone gets lodged in one of your ducts that come from your gallbladder and are connected to your liver, the pain for me would last for hours, and the doctors told me the pain was caused mainly from fatty foods (so try not to eat foods jam packed with fat! the pain attacks will go down) and even then afterwords there was a kind of "echo"-ish pain I would feel. Surgery is the best cure for the problem I felt beter after mine was removed, and now I can eat anything w/o pain! =]. Actually as scary as it might seem, you really don't need your gallbladder.