What is this painful Hard knot-like lump on head?! ?

This week I noticed a painful lump on my head. The doctor can't see me for another week. Last night the lump was swollen(size of a half dollar) and was so painful that the pain spread down to my whole head,neck and shoulders. I didnt I have this lump before. CNow this morning the lump is the size of a nickel and extremely hard like a bone or something. Its above the nape of my neck almost base of my skull. Could this be something very serious and should I be freaking out the way I am?