Feeling nauseous after eating

[Andi2020]

My dd bf told her he feels sick told her he feels sick after eating he is thin.
He won't talk to his about it he said they will say it's your own fault.
He has been called twiggy by people at school at doesn't want to be so skinny anymore wants to eat but hates the nausea feeling.
He is asking my dd for help and she is worried about him and asking me.
My first advice was for him to speak to his gp himself as he is 17 and talk to his parents.
I'm afraid if him and my dd buy something online it could make him worse if he has a food intolerance or allergy.
What would others advise.
Any good tonics you would recommend.

I think he needs help to get to the bottom of what's causing the nausea feeling i.e. if it's a mental or physical thing. If he doesn't want to be skinny then it sounds like it might be a physical issue such as allergy or intolerance. Could it even be stress related?? I really don't know as I'm not expert on such matters but his GP would be a good place to start. It might also be useful to keep a food diary and log of his symptons before seeing them.

Thanks @emmathedilemma he is going to try speaking to his mum tomorrow