Hmm. This could be a flare-up of your IBS...but how much more intense is the pain from what you're used to? Did your abdominal x-ray should anything abnormal? Was it a barium x-ray (did you have to drink the chalky white stuff)?
You should see if you can get your hands on a copy of your blood test results, as well as your abdominal x-ray and stool test results. Do you have a follow-up appointment with your doctor scheduled? The upper endoscopy and/or a CT scan of your abdomen would be the likely next step if your symptoms don't improve. In the meantime, to help your diarrhea, you might want to try one (or more) of the following "Most Popular Remedies for Chronic Diarrhea," brought to you by the lovely ladies of this forum (hey, girls, we should write a book)!
1) Calcium citrate supplements. May help soothe your tummy and firm up your poo. Also good for the bones - bonus!
2) A helping of yogurt with live cultures, such as L. acidophilus, each morning - helps replenish your digestive system with "good" bacteria.
3) Slowly adding a fiber supplement to your daily routine (start too fast and it can make you blow up like a balloon - start off easy and then work your way up from there).
There are more, but again, these should get you started!