The bowel problems of diarrhea and nausea after eating may be due to GERD(gastro esophageal reflux disease), acute non-GI infections (pyelonephritis, pneumonia),
gastroenteritis,liver diseases, pancreatic disorder,peptic disease
of upper GI tract,gastric carcinoma,CNS diseases like infections, tumors, multiple sclerosis and metabolic disturbances like diabetes and adrenal insufficiency.
I sincerely advise you to consult a physician/gastroenterologist and discuss these with him.