Oh no no no, haha the rule with snakes is no bigger then the widest part of their body, you are feeding him far to little then. Mine is just over a year old and i'm feeding him a small rat every week, you should look into rats, depending on where you get them you might save a lot of money. Rats get much bigger then mice so you will only have to buy one, where as right now you might end up having to feed him three or four mice to keep up with his growth, which will cause problems because I doubt he will take more then two in a sitting.
But yes the prey item should be no bigger then the widest part of his body, they can dislocate their jaw to swallow things much bigger then their head.
Can you post a picture of him?