3 week old kitten sick

I have a litter of 3 week old kittens, and I don't know anything about cats, let alone kittens. Anyways, they might be a month old, I'm not too sure. All of their eyes are open but one kitten. His right eye is shut, but with a little slit in it. It reminds me of when i had pink eye and my eye was stuck shut. I dont know if this is normal or if i need to take him to the vet to get him checked out. I don't really have the money to go to the vet unless its something important.

Thanks!!!

Is it gooky? Red? Weepy? How long have the others had their eyes open? Mine usually had their eyes open within a week of each other- more info, please .