6month old projectile vomits after/while feeding(going3weeks now)no fever has a diahoria(1or2 times a day)dark colour strips in the poo now,rotavirus?

Gastroenteritis: It is still possible to see symptoms of gastroenteritis after 2-3 weeks of acute infection, sometimes gastroparesis develops and propulsion of food out of the stomach into the GI tract does not happen normally. Also possible there is a behavioral component after pt has become "used to" this happening or doing it to accomplish something. If there is no fever or blood in the stool no need to worry.