Help - my son will not eat anything other than fruit and yoghurt

Hi I have a 3 year old and since he was a baby he never took to food. He eats yoghurts and fruit but that's all. The yoghurts have to be a certain brand otherwise he wont go near them and he will look before he eats to make sure.he wont even touch food. Cries if I put it near him and wont stop till I take it away.he wont sit at a table if there is crumbs on it until I clean it. If he smells food he holds his nose and cries. If i am eating a sandwich beside him he will be physically sick from looking at me eating it. I have tried everything with him and nothing works. I have had him at doctors and nutritionists and they say he's fine as he is growing normal but I am pulling my hair out. This cant be normal. He is starting school next year and would I would really loved if he had variety in his diet as he's not getting all the nutrients and vitamins he needs. Has anyone else got a child like this and have any tips or advice for me? Any help would be greatly appreciated.