I have a bump or such on the back of my head, what is it?

I have a bump or such on the back of my head, what is it?

I am having stressor responses due to this lump on the back of my neck.
Should squeezing if it is a tumor be bad or do I keep doing it until it pops?
I am considering slicing it out of me myself with a knife.
Basically, I am a bit scared.