Why does my brain feel heavy?

Just want to clarify this is not a headache really quickly. For the past 5 years I have experienced a constant weight on my brain, it doesn’t hurt but is insanely uncomfortable. The best way I could describe it is if my brain gained 5 pounds and is now too big for my skull. I don’t know if it’s mental or physical though.

For some context I’ve struggled heavily with mental illness all of my life. I am 18, and currently am diagnosed with ASD, MDD, CPTSD, BPD, panic disorder, aswell as severe anxiety.

There is momentary relief to this weight and that’s how I know it is real. THIS IS RELEVANT.When I experience physical pain it goes away. Usually to get this affect without letting my body actually be harmed, I spark a lighter just long enough for the metal around it to get hot (not enough to cause burns but enough for my brain to think it’s being hurt) and I just hold one of my thumbs on the metal bit. When I do this the side of my brain that matches the side of my thumb (left part of brain for left thumb) feels lighter.

Other symptoms include, brain fog, short term memory loss, and frequent headaches