Please help me with my lepard gecko....please asap?

ok so i bought a lepard gecko he wont eat or drink well i havent seen him eat or drink i am feedin him cricketas and meal worms he has only eat 1 meal worm. he is walkin very slow and droopy i have him in a tank with a lamp and heat mat (the heat mat is under the gl i dont think its that hot). he doesn move much at all. he just sits under his shelter. i picked him up a few mins ago and he felt cold not as in dead cold but cold enough to notice. it says the heat in his tank is 70 degres farinheight and i think he is shedding skin cause his back is going white but it looks like he is loosing color what will i do or can some 1 tell me what is wrong with him please asap