What size set up is he in?
What is the basking temp and how are you achieving it?
What type of substrate are you using and how deep is it?
Your monitor needs several things to thrive. The most important are space, security, an overhead basking temp over 130 degrees in the hot spot and a deep, dig-gable substrate that will hold humidity.
If he is not feeling secure, if he does not have enough room, if your basking site temps are too low and if you have not provided him with the appropriate substrate - he will fail to thrive in the long run.