17 year old been vomiting since 5am this morning i gave him nausea and gastroenteritis tablets not working ?

Depends on severity: Normal healthy people can get stomach flu or food poisoning symptoms occasionally. One will usually vomit until his stomach is empty, which is why it is important NOT eat or drink anything for a few hours afterwards. A common treatment is small amounts of Pedialyte or broth, maybe 2-3 ounces each hour while awake, for just one day. If worse, continued, or worrisome symptoms, his doctor can check.