What is this bumpy area in the back of my head?

Occipital protuberan. If it feels like part of your skull and like a bone it's probably the occipital protuberance and you just noticed it. If it's softer, sort of rounded and seems to be connected to your scalp it's probably a cyst, called a "wen" in the old days. Show your doctor--we like to see lumps anywhere but breasts or testicles since they are seldom serious.