hi, your son's symptoms certainly sound a bit like my life story - eating nothing but soups etc, I have a history of this going back to childhood. I think through a combination of feeling sick a lot and having gastric problems my appetite has always been shocking. When I feel really bad I retreat to eating what I think of as 'baby foods'. Not literally baby foods, but soups and things which are easy on the stomach and not heavy foods. I have a lot of fellow sufferers who do the same.

It took a long time but I was diagnosed with Behcet's disease about 8 or 9 years ago. I don't think your son has this, but Behcet's is part of a family of auto-immune disorders with the kind of symptoms you describe. All of his symptoms are symptoms I have....the pain in the muscles, inflammatory bowel issues. I really recommend you encourage your son to be seen by an immunologist. This was how I finally got a diagnosis at the age of about 42 after years of suffering. It was such a relief just to be diagnosed. Getting the right treatment has been difficult but so worthwhile pursuing. I'm not qualified to say if he has anything else going on.....you mention leukemia. I'm not qualified to comment. But I do know every symptom he has are either symptoms I have had or symptoms friends on my support group have suffered.
And I'm afraid I don't know how to get him to talk to you about it. I know some young people who are diagnosed with Behcet's. Whether or not some of them would speak to him. Would he be willing to do that? Even if he has something quite different it might be good to talk to someone about the symptoms who is suffering similarly and is in his age group.