Yes, please get a colonoscopy! You may have Crohn's Disease. That explains some of the symptoms I had before I was diagnosed (i had a wide range of symptoms) If you are not running a fever, I would not be too worried yet. I also have IBS and Crohns and know how bad that side and back pain can get. A lot of Doctors will not "put you under the scope", especially if you have an HMO. Demand it! There are medicines to help but not cure, sometimes just knowing what you have makes things a bit better.
In my experience, primary care doctors as well as some GI's, somehow do not think IBS can be so painful and disabling, even with the medicines that are out, it is awful to deal with.
I cannot believe the post that the person with IBS eats lots of fruits and veggies!! THAT WOULD MAKE THE PAIN INCREASE AND INTENSE! NOT TO MENTION ADDED BOWEL MOVEMENTS! OH MY GOODNESS SAKE! you want to baby your poor stomach. Try dry toast, plain foods, such as bread, just plain bread! - carbohydrates and no acidic foods what so ever! See if your IBS gets better with an anti-anxiety and a VERY bland diet. If so, you can learn to ease in foods that will not hurt you.
OVERALL.... if pain is your worst symptom, and not running to the bathroom 20 plus times a day, then I would definately, check your temperature when you have the pain and then report to your nearest primary care to be referred to a GI, if you can go directly to a Gastroenterologist, do that. My very first GI I ever had said to me, "you should never have to live/deal with pain, it is not normal nor natural".......
Good Luck
JH from Oregon