lump on side on neck (for ages)

[NinjaAtticus]

I'm 17 and I've had lumps in my neck for at least five years (thats the furthest back I can remember anyway), the left side of my throat feels bigger. The lump is hard, moveable and painless, when i put my chin down I can move it around under my jaw, I can also do this on the right but the lump is much smaller. I'm worried it's gotten bigger as this is the first time I've noticed my actual neck feel bigger rather than just under my jaw (although i may just not have noticed). I'm in perfect health otherwise although my family has a history of overactive (I think) thyroids so I don't know if that's got anything to do with it. Does anyone have any clue what it is and whether I should get it checked out?