What Does A Lump On The Neck At The Base Of Skull Indicate?

I've got a knot like lump on my neck to the base of my skull, just to the left of my spine. Its been there a few months but lately its been hard move my head without discomfort and I've been getting mild-moderate headaches quite frequently which is not normal for me, massage a does not seem to be making a difference to it. Is there something else I could do to fix it as I am not sure what it might be?