I have 3 crested geckos that were purchased at the same time and are all roughly the same age. (3-4 months old as of today) I bought them about two month ago when they were about 1 and a half months old. Two of them are doing well and have about doubled (maybe even tripled) in size. but one is still about the same size as when I got him/her. I know he/she is eating because it poops like crazy. What could be the problem? Is this one just growing at a different rate?