My youngest is autistic along with other diagnoses. He’s 8 years old and only 53#. He sees a nutritionist and a feeding specialist. He is not malnourished and is extremely picky eater. Sudden vomiting wouldn’t be from eating if his eating patterns haven’t changed.
Digestive disorders are present in around 70% of autism cases. If it’s a chronic issue and not just a few days (stomach bug) then I get him into a pediatric gastroenterologist
Does he vomit all the time? If so it could be from the food or he could just have a stomach bug or something. Have you talked with a dietitian, OT, and speech about working on getting him to try new things? Will he eat the nuggets that are made with veggies or sweet potato or cauliflower fries? You can also get pasta made from veggies. There are lots of tricks to try.