FWIW (and not to stop you from getting a colonoscopy—you should!), I have had symptoms like this on and off through adulthood (20 years or so).
For this reason and a couple other IBS symptoms, I've gotten two colonoscopies, one capsule endoscopy, and one sigmoidoscopy in my day. And all have come back negative for anything whatsoever.
Again, if you've got symptoms, see a doctor. But if you're like me and freak out at everything and assume you're dying at the drop of a hat—it's likely not something awful.