What Causes Chronic Swollen Lymph Nodes In The Groin Area?

My 25 year old son has been having chronic health issues with cysts, infected hair follicles, swollen lymphnodes ---- all in his groin upper leg mid body region --- AND chronic stomach aches, cramps, some diarrhea -- these things have come & gone often over the past couple of years. He's been feeling stressed over the past 6 mos. at least, & it seems these issues have been happening more often. No fevers. He's had blood tests & ultra sounds, been given lotions/ solutions to use to clean his legs, etc., but no one can seem to find anything that can prevent his problems from happening over & over. Why would someone keep getting swollen glands in their groin & lower abdomen like that? He works at a gym & works out everyday with weights, etc.