I'm feeling much better right now...but just in case...
you should go to the hospital and get it checked out. If its the inside of your head hurting, like an intense migrain, then get it checked out. That happened to me before and it turned out to be a tumor so go see a doctor.
Tumor

It's mostly the back side of my head.
Walk daily. Sign up for sports. Don't stay in the house all day, go out and hang out with friends, or go out and walk around the neighborhood. And watch your eating habits too.
I did do water polo until 2 weeks ago since it's over. I think I eat pretty healthy since my mom is kind of a health freak at times which means no soda, hamburgers, fries, any kind of fast food, greasy foods, etc. blech. She's big on drinking water, drinking milk, and eating lots of fresh (organic if possible) fruits and vegetables.
The back of your head? Like maybe your neck area? In any case, I think you should go to the doctor to get it checked out.
Yeah...like it felt...bad?

I can't explain it...it just hurt like crazy.
Can there be a reason to your headache?(Or did it just start out of nowhere?) Maby you fell the day before and hitted your head? If so, go see the doctor.
I dunno...I had the same headache before I went to sleep at night and I was like, oh well...it'll probably go away and then it was like BAM when I woke up from it =(
I probably should :x
if its intense, and doesnt seem to get better over the night, go ask a doctor, something lik ethat isn't a nice thing to play around with :X
better safe than sorry

It's like better right now. Yesterday it was kind of bad and when I woke up today it got better. I wish I knew what it was though.