Thanks for your help. There is no chance that he could of eaten gravel, as there is no gravel in the tank.
He hasn't been eating for a week, i changed the tank about 3 weeks ago, but he was eating fine after that.
I usually feed him meal worms(i read that you're not suppose to, but the pet shop told me to feed him that) recently, the last few weeks i have fed him earth worms, 2 crickets, and yeah can't think of anything else.
He usually gobbles up his food straight away, (probably because i don't feed him enough, i usually feed him only 3 times a week, but he eats a lot in those 3 feeding)
I tried feeding him again (his favourite, earth worms) he just moves his head away from the food.
I am really worried, what should i do? Thanks again for your help.