As said above, it's probably nothing serious. Eat more fiber. Eat fresh, raw vegetables daily, if you can make yourself do so. Fruit is good too.
I've experienced this before, and it was not anything to worry about. Just a little painful and annoying. In my case, it was caused by diet. Lots of protein and not enough fibrous carbs to help process it all.
And as said above, and not to be ignored: DRINK WATER! It is extremely important. Your body needs a minimum of 1-2 quarts of water per day, preferably more if you're physically active. Drink throughout the day, sipping whenever you get a chance, rather than trying to take it all in a few giant glasses. Your body can only process about 8 ounces per hour, so you need to drink throughout the entire day. This is important for your pooping

but also very important for many, many bodily functions. Water is life.