These can be a side effect of Celiac desease, its where you are allergic to the wheat/gluten in foods like bread, pasta, even gravey and other sauces. Anything that has been bathed in sauce that contains gluten like certain salad dressings, sauces they use to cook vegatables in can cause very nasty pain, bad IBS and nausea. The gluten causes your intestines to eat away at themselves because of the allergic reaction. Usually not discovered or testable until mid teen years.
I've attatched some links for you to read up on Celiacs Desease, if you think you have most of the symptoms it wont hurt to mention it to your Doctor.
Google Search Results for your research:
http://www.google.com/#hl=en&q=Celiac+Disease&aq=f&aqi=g10&aql=&oq=&gs_rfai=&pbx=1&fp=634be7f9c98ae18c
Celiac group on MedHelp -
http://www.medhelp.org/forums/Celiac-Sprue-Disease/show/226