Cleaning silver but still keeps getting dull!?

So i cleaned my silver necklace with toothpaste qhich worked fabulous! But than after a couple of days in which i did not wear it i hung it on my jewlery holder it became dull again! It was literally less than 4 days of just sitting there! So my question is how do i keep it to stay shiny without having the need to clean it every time im going to wear it?