It looks like you need to read the "Worth Reading for IBS'ers" Thread at the top of the list of Threads. It will talk about the Rome Criteria for diagnosing patients with IBS. That way you can be the judge.
But, from what you've said, it does sound like IBS. However, you should probably consult with your GP, because IBS is a general term used after all other disorders and illnesses have been tested for and show negative. i.e. It is a disorder that is diagnosed by exclusion.
Well, I hope this helps you some.