The more you think about it the worse it will get, I promise you that. Just stay strong and don't stress out about it. Visit a doctor when you need to. Headaches (especially if you get them all the time) come from a lot of things, including common things like allergies
If it were a brain tumor, you'd be feeling a lot more than just a headache, believe me.
There's nothing wrong with being concerned about it, don't beat yourself up over it. Anxiety (at a normal sense
) is what keeps us alive.