Having symptoms & can not find an answer for constipation & full feeling after eating,loss of weight

My 41 year old son is having cronic constipation & can not tolerate solid foods very well. Has a feeling of fullness after few bites of food & drink. He has lost weight & suffers with some pain. The basic test have revealed nothing. He did have a cancerous mass on his left kidney removed. They say the kidney mass had nothing to do with his other symptoms & have refered him to a teaching hospital UAB in Birmingham. Has anyone had symptoms similer to this & what test revealed your problem. Thank You.