Bump on my head, need advice

A couple of nights ago, a bump appeared in my head. (It’s almost on the back of my head, but not quite.) I didn’t hit my head at all before this. The bump hurts to lay on and if it’s touched, but it is also actively sore without being touched. It’s raised to about 2 stacked quarters’ thickness. (Sorry, I didn’t know how else to describe it 😬) My partner says it’s reddish brown. It has some flakiness, but not much. I’m not sure if this is relevant at all, but the bottom areas of my skull are tender today. Does anyone have any idea of what’s happening?