You may want to check out the symptom page for IBD to better determine if your symptoms sound like Crohn's or Colitis. The Irritable Bowel Syndrome page may also be useful.
I have found it helpful to use a journal to keep track of foods eaten and symptoms to see if there are any obvious triggers. Taking this list to your physician can help them to better determine if you may be dealing with food allergies or intolerances as well. Be sure to bring your food/symptom journal along with a complete list of your medications to your appointment.
There are numerous other reasons for GI upset so please discuss the problem with your physician.