My Son, 19 Yrs. Old Is Having Stomach Pain And

My son, 19 yrs. old is having stomach pain and extreme fatigue. He's had lots of tests - still trying to figure out what is going on. I'm pretty sure they've ruled out H.Pylori and C-diff - does that mean he probably doesn't have an ulcer? Also - he is so tired and uncomfortable, had to drop his college classes. The doctor mentioned possibility of Crohn's. How long do the stool tests take to diagnose Crohn's?