Aww I completely understand about the exhausted from worrying feeling. I'm there all too often lately.
First of all, that doctor was a complete jerk (to put it nicely) to treat your fears with such nonchalance. A person like that should NOT be practicing medicine in any capacity. I can't believe he said those things to you! I would've cried right then and there.
Second of all, the headache in the back/crown of your head sounds a lot like a tension headache to me, which often happens from muscles tension in the neck (the knots in your neck). The pressure you in the roof of your mouth felt when lying with your head over the table could be a separate sinus issue - you may have just had some excess mucus up in there and didn't realize it. Honestly, I really think you are completely fine. Tension headaches are extremely common. If you had a brain tumor you would not be WONDERING if you had a brain tumor. You would have balance/coordination issues, visual disturbances, hearing issues, etc depending on the location of the tumor. Even those things have other more likely causes than a brain tumor.
I really do feel for you and your anxiety. I've been a regular poster lately too because I'm constantly hopping from one death sentence to another - not flippantly, but truly feeling like "this is the one that's gonna get me" kinda mentality. It's totally exhausting and debilitating. I just started 20mg of Prozac and hoping that will help end the circular thinking.