I was diagnosed with IBS 20 years ago and it sounds like the same thing. I have had all of the same tests and without Immodium daily, I had diarrehea after EVERY meal. The only thing that has made a difference is a gluten free diet. Have you tried that?
I can't help you- i am new on here and seen your post because your systems are similar to my husbands.We have done all those tests as well that you have, and just came up with inflammed intestine or mild gastritis. But he doesn't have the diarrhea. Constipation is more of that issue. He has server pain all the time. It is unreal! He gets very tired-passes out if he sits after work on the couch, and when he has bad attacks he has bad headaches and he has to make himself throw-up just to get some relief from the stomach pain. He has gas and bloating, I have to push on his tummy so the gas may have a chance to move. And every so often his breath smells like sewer! Crazy- because it will be completely gone within 10-15 minutes! It just comes and goes. It is horrible for me to see. I cant imagine how it is for him and even for you evey day... I am just worn out from the expenses and no solutions. Tired and frustrated. And I am not the one who is sick with these issues. Good luck with someone being able to answer you. I hope the same for me! Best of luck!