Gastrointestinal specialist might have an idea
Could try an oral saline solution to clear your intestines. I think Fleet makes one, or the store might have a generic of it.
I went to a gastro guy when my stomach was all kinds of fucked up for a couple of years and he told me to drink the whole solution before he did a colonoscopy. Had to drink a lot of clear liquid with it (sprite/7-up for when the solution is drank, tastes terrible, but no problem following the solution up with water). I think I drank a 2-liter over the course of a couple of hours and followed with some water for the next 4 hours or so (though not as much)
The solution basically makes the liquid just run through your intestines, so you must HYDRATE THOROUGHLY TO AVOID DEATH. You'll get some burn with it too, I suspect from stomach acid that makes its way through with the liquid. My stomach has been way better since then. You'll shit all kinds of nasty a couple of times, then you'll basically just be shitting water (and whatever bacteria it happens to snag watersliding through your intestines).
Note that the bottles say to only take the recommended amount unless you are instructed by a doctor. And I'm not a doctor. I also would not use it regularly. Read the instructions that come with it.
Could also try some stuff like TUMS/Pepcid AC / Prevacid (sp?), but I think Pepcid or Prevacid need time to build up so that might not be a solution that gives you an immediate indication if that will help whatever you have wrong.