Need hamster advise and incite!?

ok i have asked this question plenty of times before but i want to know if i am getting correct information. my hamster has a small bump on his neck that can move if pushed on, is small as a nerd (piece of candy), hard, and not visable just by looking at him.... its actually not really a bump because it feels like a beed or something underneath his fur that can move like if you push on it it goes away from your finger... yeah what could it be?