I suffer from IBS. I hate to be graphic but I have had the exact opposite problem for years now. But when I was a child a teenager I suffered from constipation. I wouldn't go for days to a week was the norm.
What I can HIGHLY recommend is eating a bowl of the original Fiber One cereal every morning for breakfast. You may need to supplement with another bowl during the day for the first week to kick start your system if you really want to get things going. Or you can try the bars. I hate to sound like a saleswomen but trust me, it works. Again, I hate to be graphic but my husband and I both ate the cereal as part of a diet to lose some extra weight and we were going like 3x's a day. I have no idea where it all came from. LOL! My sister-in-law ate the bars and was telling me about it also. It's just not as much fiber as the cereal.
I'd give that a try before any more medicines any chemicals, doctors, and tests, etc. We really do not get the fiber we need everyday.
Good Luck!