I have a theory. I think it may be helpful to look into Crohn's Disease. The primary symptoms are abdominal pain and loose stools. From reading all the posts on this website, it seems there are a few things that could point to it. First, a symptom of Crohn's is mouth sores/ irritated lips; other people on this site have been cured using Imuran, a treatment for Crohn's disease. Additionally, success has also been seen with the use of Vitamin D, which has a known correlation of deficiency in Crohn's disease patients.
I'm no doctor, and this is all speculation, but definitely something to look into if you're having stomach problems as well.