A brain tumor causes serious headaches I think. But if you have a history of migranes then this is probably migrane activity. I get it all sometimes I'd rather have a headache then the pressure. I always get it on the right side too but that's where the migranes live too. Feels like your eye has something behind it without the pain. In a few days I may get a headache but what I do is start taking tylonol before the pain hits.
Also could be your sinus you have sinuses all through your skull not just in your nose.
Also could be jaw pressure from TMJ , do you grind your teeth when you sleep ? TMJ headaches ( I get me all yay for me ) hurt as bad if not worse than migranes.
Migrane activity does not always involve pain. I also get ...the fairys... Little sparkely lights in the outside of my vision. No pain with these but get dizzy sometimes. I get the weird pressure in my head too.
Try a sinus headache med OTC and see if it helps to rule out sinus pressure. TMJ press on your jaw joint a little on the right side of it is tender then ask the dentist for a referral to a TMJ specialist.
But it didn't sound like a brain tumor to me BUT I'm not a doctor.
Let's us know how it works out.
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May the Force be with you. ??