What Could Cause A Lump Behind The Neck And Another On The Crown With Pain Running Down Between Them?

Hi. I have what appears to be a hard, pea-sized lump at the base of my skull, and to the left side of my spine. It is tender to the touch, as is the surrounding area of skull above the lump. I also have what I thought was a sebaceous cyst at the crown of my head, and slightly to the left, which has recently become inflamed, and the tender, bruise-like pain runs from the lump on the top of my head to the lump located on my neck. What could this be??