My stomach is bloated and hard ? Help :(?

Well I'm 15 and no I am NOT pregnant, I don't even have a bf. So that's not it. Anyway, I've been going to the loo properly and thats fine too, so it's not constipation. My tummy has been bloated for about 3 / 4 days now. And my diet is healthy, I eat quite a lot of fruit and veg.. So what could it be? And how can I get rid of it? My tummy is usually natrually flat :(