I understand that this must be really difficult. I have a 19 year old, and luckily thusfar, he's fine with me coming to the doctor with him, and he has signed releases so that doctors will speak to me. Not knowing your son, he may or may not ok you coming to the doctor's apt. Is it possible for you to negotiate to come in to the exam room for the first 5 minutes or the last 5 minutes? If not, perhaps could persuade your son to mention the family history and ask for some screening blood work- cbc, c reactive protein.
Since many people are fatigued and have various aches and pains, doctors often don't take notice unless there are red flags by history (fevers, blood in stool, weight loss), physical exam or labs (anemia, increased inflammatory markers...). This is why it is so difficult for people with IBD and normal blood work to get the diagnostic tests (endoscopy) needed to get a diagnosis.
[The doctor at my son's school said his symptoms were most likely stress. I asked her to check some blood work; it was only when he was found to be anemic and have a CRP that the doctor thought there might be something to investigate. Even the gastroenterologist said sounds like IBS so I interrupted and said, "but you don't see anemia and elevated CRP in IBS, do you?" He then recommended an endoscopy which showed Crohn's. ]
Hopefully, your son doesn't have IBD, but considering the possibility is a good idea.