Hi- Soluble fiber is in foods such as pasta, rice, oatmeal, potatos, and certain breads. Insoluble fiber is like straight out bran cereal, and some vegetables amongst other things (basically the fiber you would use if constipated). If you read 'Eating for IBS'- a pretty widely read and popular book, the author (who has suffered from IBS since the age of 9) tells you to always start with a soluble fiber first when on an empty stomach and then follow with other foods. Although I believe that this is supposed to be more helpful with IBS-D sufferers. Now the thing with insoluble fiber is it's great for bulk and for constipation and some people have success with it, it can also be the cause of episodes of D IF you are prone to that. You'll need to ask your MD to be more specific in terms of what he wants you to try.
Also, it doesn't sound like you have an official dx yet, so after the colonoscopy is when you'll really have some answers about what may work. Others on this site try daily products such as citrucel for bulk (which is a powder form of insoluble fiber - the chocolate flavor I find pretty tasty!) I'm sure others will comment too- I hope you find it all helpful. Good luck.