You have tight neck muscles on that side causing the pain. The neck muscles go to the top of your head so they cover a lot of are that they can hurt when they are tight. Freeing up your neck muscles will release the tight ones causing the pain and here's how to free them up:
Place your hands behind your head so your fingers meet in the middle of your neck. Press into the neck with a moderate pressure and hold. After 30 seconds slowly lower your head as far as you can, then remove the pressure from the muscles but continue holding your head down for another 30 seconds.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.
Dear, it will not be a brain tumor.Do not worry.Maybe you're just a cold.