Hi worrywart. Be thankful your colonoscopy did not show something more serious than IBS. That said, IBS is a real downer, and yes, you can feel pretty bad with it. Some days you may feel really good, but stress or just a general "flare-up" can ruin everything again. Fiber is a great place to start; fiber is a bowel regulator, therefore, it works for both constipation and diarrhea. It doesn't matter what fiber you use, but a natural fiber like Metamucil is better for your system than a synthetic fiber like Fibercon. Be prepared for a few days of increased gas/bloating as your body adjusts to increased fiber.
Keep us posted on how your doing; we're all here to help.