HELP ME SOMEONE WHO IS GOOD WITH ANIMALS

Okay so I recently got a gecko and he has everything he needs in the tank hot cold side and the right food and calcium and he ate fine then started to regurgitate his food and just will no longer eat, as you can see by the difference of both pictures that he’s gone really dull. He doesn’t need to shed as he did not that long ago. Can someone help what to do NO STUPID ANSWERS