Why do my hamsters always die?

welll i've had three hamsters, and all have died. my first one i had him for like 3 days and then he stopped eating, and got wet-tail :( i was rly sad tht i did something wrong but i think he got it from the petstore.my 2 hammie i had for a week, he died suddenly tho, i found him one morning while i went to feed him and change his water he always comes out so i checked on him. he was curled up in a ball where he sleeps his head was so flat. i didn't know wht i did! so again i cried :( i don't know how he died!!! my 3 hammie i had for 2 weeks or more.i loved him so much, and one night he started shaking and wouldn't eat. he look so horrible i started crying so hard, so i added extra bedding and he walked over to it and felll asleep. every hour i would check on him to c if he was alive. at around 11:00pm i found him in the same spot dead, i cried my self to sleep tht night praying for him. he was so good all of them!!! :'( i miss them all and i don't know how the last two died their names 1.curly,2.louie, and 3.peaches. i loved them so much and i feel that their dealth was all my fault. do u know how the died or wht i did wrong. thanks for the answeres! RIP Curly,Louie,and Peaches, love u all<3333