I know it is kind of a funny topic but sucks when it happens to you. I had the same thing happen one summer and I was in the same boat as you. Nothing I did seemed to help. I went to the Dr., had all kinds of tests, changed what I would eat the night before, etc. Nothing. Finally it just stopped happening on its own and never happened again. So, bottom line (no pun intended) I never could figure it out and hopefully it will just go away for you after a few weeks. Sucks to have to plan your runs so that you go by porta potties several times though--or at least some dense trees.