Hey,
First of all, how big is he snout to vent??? He might be growing just fine and you don't relize it.
Also, as they were saying, make sure you give him protein. It doesn't necesarily have to be roaches, just make sure to give him plenty of protein. You CAN supply your cham with ONE food item his entire life, and he will recieve all the proper nutrients he needs, if gut-loaded, and supplemented correctly. Many people say that a varied diet is the only way to provide a cham with all the nutrition he needs. This is not the case, IN MY OPINION. Whehter or not a cham will get bored with that same food item day after day, depends on the individual. To supply a cham with protein, simply buy some fish flakes, and offer them to the crickets 1-2 hours before offering the crickets to your cham. Here is a link of where to buy a 5 pound bucket!!! It is expensive, but is well worth it. It will last you quite a while.
http://www.drsfostersmith.com/
It is somewhere under "fish", LOL.
However I have heard people saying that recent studies show that animal protein is bad for chams. I honestly do not believe this, but you can believe what you wish. That is just my opinion, and why I am posting the link. If you prefer to not use animal protein, I believe that alfalpha is a good non-animal protein source.
Ank-Inc.
Adam.