I just wanted to let you know that I was having the same symptoms. My bms would even get flat and rectangle shaped. I was TERRIFIED that I might've had colon cancer so I went to my dr and told him my symptoms and how scared I was and how much it was stressing me out, so he scheduled a colonoscopy, and everything was normal - I have IBS-Constipation.
A couple of questions: Have you been under stress here lately? How long have you been having these symptoms? Have you noticed passing any mucus in your bms?
Stress in your life or anxiety can actually bring on IBS. Passing mucus (with or without any poo) is a sign of IBS (sometimes all I would do is fart, and would pass mucus) The mucus is a clear, yellowish color and has a strong oder.
The best thing I can tell you to do is go to your dr and demand a colonoscopy be done because it is not healthy to worry and wonder what's going on inside your body.
If you haven't tried yet, get yourself some "bulking" fiber supplement. That may add some "body" to your poo and make you feel a little more relieved after you go.
Best of luck...your first step is making the appointment. After you do that, just try to put it in the back of your mind until you know for sure:)
"Success is the ability to go from one failure to another with no loss of enthusiasm."
– Sir Winston Churchil