My leopard gecko is not eating!

About a month ago I got a leopard gecko, he was eating fine but then he started regurgitating and then last Saturday I cleaned his tank and picked him up for the first time since I got him and he was freaking out and then jumped onto the carpet on my floor out of my hand and then when I but him back into the tank after cleaning it he was really nerves and was trying to climb the walls and stuff and since Saturday he will not eat, he drinks normally and is active at night but he just ignores the crickets I try to give him. Tomorrow im getting a better light thinking it might be the temp in the tank he has a 50 watt buld right now and his temp in the tank on the warm side is in the 80s im thinking that might be the problem when he was regurgitating. His tail now is kinda thin, im really worried and need help.

There can be several reasons for this. You're right to monitor the temps closer, as this could be the cause. Other common causes are worms and calcium deficiencies. The best idea is to start monitoring all of this more carefully. Make sure you're dusting food items exactly as directed, and temps are precisely in the right range. Usually a $60 to $70 vet visit can take care of checking and treating for worms and other parasites if heat and calcium don't resolve your problems. If he's lost a lot of weight and you're worried about putting weight on him quickly you can force feed him using a recipe called Marcia's slurry, which you can find by doing a search of the leopard gecko discussion forum. I used it and it was very helpful. It can also kick start some anorexic leos into eating on their own if they still don't eat after you solve the original cause of the problem.