Why am i so skinny even though I eat so much?

I'm a 16 year old boy and i'm 6"4' (195 cm) and 55 kilos. every day I eat a ridiculous amount of food. for breakfast i eat 14 wheetbix, for lunch between 4 and 8 sandwiches and for dinner often three servings, plus I snack continuously between meals. I barely exercise and when i do I struggle to put on muscle. why is this?