Welcome to healingwell.com. A lot of people start getting headaches in their teenage years, some due to stress but a lot of the times it is a change in horomones that will "trigger" or set off migraines. I definitely would see a doctor and make sure there is nothing more serious going on that you just can't see.
I, again, highly doubt the presence of a brain tumor. You would have other symptoms and rarely are headaches a sign of brain tumor. As far as waking up saying something like you have a brain tumor I would imagine is not too far fetched to FEEL like there is something really wrong. I know this sounds weird but when I have a really bad headache I dream that I have been shot in my head or stabbed etc.
See a doctor and let us know how things are going.