What size and type of enclosure is he in? And where is the enclosure located? (Is it in a busy or noisy place or drafty place?) How often do you handle the snake? And how often are you tweaking and changing the enclosure?

So long as the snake is maintaining good weight, he'll be fine. Be patient and persistent and don't get in too much of a hurry to "make" him eat. Doing so tends to make you go backwards instead of fowards. Get the environment as secure as possible...with the temps and humidity maintained as consistently as possible....and then simply be patient. Don't handle him until he's eating regularly for you. Don't offer food too often. Just once a week.