Possible causes would be malabsorption, any type of
infectiousInfectious endocarditis
Infectious mononucleosis
Infectious mononucleosis #3 diarrhea (especially Salmonella given the history of undercooked chicken), inflammatory bowel disease (less likely given the negative colonoscopy), or irritable bowel disease.
To test for malabsorption, you may want to consider blood tests looking for celiac disease, or testing for fecal fat content (which can suggest malabsorption). Another consideration would be sending off the stool sample for culture, to ensure there is no infectious cause.
As for irritable bowel disease, increasing fiber in the diet can be helpful. I would discuss these options with your personal physician, or consider a GI referral.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b