I also worry about cell phones causing cancer. In fact, I walk away from the microwave when I heat up food, try to not take deep breaths in a place where I suspect asbestos, and put my cell phone at least 5 feet away from me when I sleep, but I am a worry wart and I know it. I was watching CNN and there was a segment about cell phones and brain cancer. Dr. Sanja Gupta (spelling??) said the only thing they could find was that cell phones just activate your brain cells and they don't know if that's good, bad, or neither. He said he personally uses a little headset when on his phone because he uses it a lot... just to be on the safe side. I think you are fine. You could possibly have migraines, not have enough water, or maybe the stress and worry could be causing your dizziness and headaches. I don't think you can even feel much pain if you have brain cancer or tumor until much later on anyway, and your dr. would know if you had it by then because of many other symptoms and not just from the headaches.
I also get a lot of headaches and take daily migraine medicine. I wasn't always like that, but it just started up when I was maybe 12 years old. Some people just have that. Another explanation could be growing sinuses (which happens mainly in your teen years). The most likely, I think, is that it's caused from stress, so take it easy and don't worry about it...I know it's hard to stop worrying, but consider maybe having a relaxing spa-ish day to just relax, take a nice warm bath, and eat yummy fruits and stuff.
Hope this helps!