What Causes Pain In Lower Abdomen Radiating To The Back?

I am a 22 yr male, college student, varsity football player. Two years ago I was admitted to the hospital for possible appendicitis (expercienced severe lower right side abdominal pain and severe vomitting) but was diagnosed with gastroenteritis and mesenteric adenitis. Since then I have had chronic abdominal pain always right side that sometimes feels like it radiates to my back. I also have had chronic diarrhea since then, sometimes small pellets, but never normal. I have exprienced fatigue, sometimes extreme. I also have skin issues - peels off hands and feet, sometimes little red/rashy spots. Lower back pain and stiffness, but also have mild scoliosis and spondyolisthesis diagnosed at age 16, asthma also diagnosed at same age. Sypmtoms flare, always present but everything gets worse with flare. Occaisional chills, chronic low nausea but sometimes bad enough I vomit . Had to give up football, because of weight loss and inability to gain weight, plus back inflexibility and fatigue. Was 290-300 at hospitalization, now can t gain and weight between 240-250. I m 6 4 with large frame. Have had colonoscopy, upper endoscopy, MRI of abdomen, CT of same, all normal. WBC from two weeks ago was 19,000, didnot have high WBC last July. Some stool tests done, all normal. Still waiting results on tests for bacterial infection and urinalysis.