Why does my silver chain keep tarnishing?

I have had the same sterling silver chain and charm for over 3 years and never had to clean it until recently, when it suddenly turned black, very quickly. I got some liquid jewelry cleaner and cleaned it, following the instructions. It was only silver for about a day before it turned black again. I tried with a silver cleaner that was paste, recommended to me by someone as the best silver cleaner they've ever tried, and it did the same thing. Then I tried a silver cleaning cloth, and it did the same thing. Shouldn't it stay silver for longer than a day? What's wrong with my chain? What can I do to keep from having to clean it every single day?