What Causes Intense Stomach Pains Occasionally?

I have a fairly intense pain in my stomach occasionally after only some meals. It doesn't feel like nausea. I would describe the sensations as either:

1. Internal bleeding in my stomach
2. Really sore (like from laughing really hard for really long)
3. Burning sensation (like I hate some really hot peppers)
4. Stomach cramping

It comes on about 30 minutes after eating only SOMETIMES and can last anywhere from 3 to 5 hours. I have no idea what could be causing it...Stomach ulcer? Something to do with my stomach lining? Something I eat? It's not nausea.

Any help is much appreciated.