Fear of a brain tumor is what kicked off my HA and it was
not the place to start. I really would've preferred easing myself into it. I went through all the symptoms - dizziness, vision problems, light-headedness, tingling, perceived weakness and shaking - and it turned out to be a combination of allergies and anxiety. The brain tumor hole is a really difficult hole to climb out of, too, so I can totally sympathize.
You don't say that this is what you're thinking, but I know well how irrational we can be when in the depths of an HA episode, so I'm just going to say it - you won't be able to feel a brain tumor with your fingers. It might be a bump you've had all your life (scalps/skulls can have bumps) but never noticed until now, when you're hyper-fixated on the area. It's also probably not the cause of your headaches, unless you banged your head at some point in the recent past.
You know what
does cause headaches, especially at the top of the head? Anxiety. The contracting of muscles, which we often don't even realize we're doing, can really hurt after we've been doing it for a while.
You sound like you have a great doctor, and I hope with her help you can pull yourself out of this