First thing first: if you're taking your gecko out that often, you should propably reduce handling to a minimum of what is necessary. That might get him to eat more, since taking out a gecko always stresses them, no matter if they show it at the same time or not.
Second thing is: you should not keep him on sand only, it's bad for their ankles and the avoid loose sand in the wild as well. Try to get some bricked earth powder, you can mix it with the sand (4 or 5 parts sand, 1 part bricked earth), fill it in the tank while it's still wet and wait for it to dry. It get's pretty hard, sometimes they still can dig in it, and it doesn't get thrown around that much. It's a better way to build a more natural environment.
Other than that, could you show us some pictures of your enclosure? I'm curious to see how your geckos tank looks like.
yours,
Fabrizio