Severe pain when I touch lower back of head on left side

Hello!

For years, I feel pain when I touch the back of my head on the lower side (on my left).  That area seems to be slightly bigger than the same section on the right side.  I've had this pain for years but it won't go away.  Do you think I should see a doctor about it?  What might be causing it?  Years ago, I had several cysts surgically removed from the top of my head but the last time was about 1 year before this pain started.  I have not had any new cysts lately except a small one on top of my head and this bump is NOT a cyst (aka "win") because those never caused me any pain and those were smaller.

What could be causing this?  Do you think I need to go to a doctor?  Do I have a brain tumor??