I've only had my corn snake for about 2 weeks and ive only seen it drink once?

i have a 20 gallon tank, with a warm side nd a cool side to it. i keep the water dish at the cool sid eof the tank, but my snake always stays at the warm side, and i rarely ever see it move. he eats regularly, but i've only seen it drink once, they day i got it. his eyes r turnig whiteish bec he is going to shed soon, is this y he wont move much?? i can hold it perfectly fine, moves around alot whn i hol it, but whn i put it bck in the tank he jst crawls back to his hiding place nd just sits there all the time. i see his place changes now and again when i get up in the morning, do they tend to move around more at night?? or mostly just when im not paying attention, bec im not in my room all day, but always when i get back in my room hes in the same spot at that rock just a diff position. my snake isnt very big, only about 18 inches, just wondering if maybe the one side of the tank isnt warm enough and the snake just doesnt get warm enough to move, or bec its going to shed jst doesnt feel like moving, or mostlikly, moves when i am not paying attention nd i prob have nthing to wrry about?? im a first time snake owner (abviously) and i just dont want my snake to die on me or anything....any extra tips on corn snake care would be greatly appreciated..thnks :)