Painless, hard immovable Lump on my Neck?!

I have a lump on the back of my neck .. aprroxomitaely on the lower neck... It's hard and painlesss. I've had it for about a year now.. it started out small, but now its a lil bigger then before. What could it be??? I'm really scared. Other then this lump i don't have any symptoms of being sick so i'm not sure what it is.

Thanks for the help!