How long has this been occuring? If the pain is constant, and it doesnt get any better, or go away in a few days, go see your doc. You will probably get an ultrasound.

It's just been today, but it hasn't stopped hurting. For work I had to wear pants that come right to my navel and may have put pressure on it and it hurt worse there. I've been trying to do some research and it may be a hernia... Do 15 year olds get hernias? Does this sound like a hernia to you?

Hernias are more common in males than in females and there would be a protrusion. Is it a surface pain, or does it feel like it is more deep. You may have pull a muscle or pinched a nerve, or it may be underneath, where your uterus or bladder is. When was your last period? And are you sexually active ? Have you noticed any other symptoms?

It definatly feels like it is something inside me. Its not like a bruise. My last period was 2 days ago, but it was a breakthrough bleeding. I only have my period every 3 months or so, and about once a month I bleed for a day and thats it. I'm not sexually active and I havent noticed any other symptoms.

What could it be if it were where my uterus was? An infection or is it possible that it's an ovary cyst?

If it were an ovary cyst you would feel it to the left or right of your belly button, not in the center.Since you have irregular periods, and your last one was only 2 days ago, I would say that it is just cramps to do with menstruating. It's common for girls to have irregular periods, especially when they are younger. It's not that big of a deal, as I know some girls who are 18, and still have irregular periods. If I were you I would see a doctor and start birth control pills, even if you aren't sexually active. The hormones in the pills will regulate your period like clock work. It also helps some of the symptoms of periods such as cramps, bloating, pms etc. It can also help acne, if that is a problems for you.
Hope this helps

My cramps are usually below my belly button, but that might just be me... Certainly go to a doctor, just ot get it all figured out and fixed, if it doesn't go away in a day or two. No sense being in pain!

Cyst don't just happen on your ovary. They can happen on your uterous. You won't know for sure that until it burst or go to the doctor. Hope by now that the pain has gone away or that you know what it is.