I'm 18 years old and weigh around 8 and a half stone wich I think is pretty normal for my age and height etc.. And I'm normal sized everywhere but my stomach. It looks like I'm constantly bloated, it sticks out so far, its like all the excess fat/weight/flab whatever, just goes to my belly.
I eat normally and I'm active.
Does anyone know why this is and how to stop it?

A big tummy is usually the sigh of too much refined carbs. Try cutting out all the white carbs (sugar, bread, pasta, rice, cereals, potatoes) and eat more protein, fat and green vegetables. Base your diet on fresh whole food, not low fat diet products or fast food.

However, it's important to be realistic about your tummy. Very very few people have a completely flat tummy. And as we can see it so easily, most of us are convinced our tummy is far bigger than it is.