Three week old kitten died

I have a cat who had a litter of kittens(3 kittens) and one of them died. He had stopped eating for a few days and all he did was sit and cry, he would sit in the corner of the kittening box and cry with his face in the corner. He seemed healthy but I guess obviously not.. If been doing research as we didn't have enough money to take him to the vet and I left home for a few hours and when I came home he was dead..
I know I can't be given advice on how to care for him, but I would like to know if it could've been from me, or if he was sick. I don't know what details to put on here to be told what the cause was, but just ask and ill tell. I like to know the causes and if the other two kittens can get what he had. I am heart broken over losing him so please any answer will help..
Thank you,
-Caitlyn.

I am so sorry you are heart broken. Kittens can pass away from so many things I don't have much experience here but a lot of others do and can tell you what signs to look for. Please let us know how old they are.

3 weeks, they're still nursing they'll be 4 weeks on the 10'th

It's so sad, but the truth is that sometimes kittens die for unknown reasons. It could be genetic, he could have a physical reason, such as a deformity inside somewhere, or a million different things. Watch the remaining kittens closely. I had kittens get distemper and die one by one, it can be heartbreaking. Has mom had all her shots? Even one series helps. If another falls ill have a blood test run to check for disease, or at least call a vet and describe the symptoms and that another kitten had died. One may take pity and have you bring it in.  You might weigh them daily to see if they are getting enough to eat too. All the luck, and keep us posted. I'll pray fro you all, and I'll pray that that sweet innocent baby made it safely to the Rainbow Bridge.