Jojo, if this happened after taking antibiotics, consider trying some probiotics. Antibiotics are great for killing things off, but they also can kill off the good bacteria we need in our digestive tracts. Replenshing it might help. There are a number of good brands on the market that include Culturelle, PB8 and Digestive Advantage-IBS among others.
But you should still check with your doc to see if there is anything else going on that could account for the symptoms you're having.
It sounds like you are having a case of constipation. Fiber doesn't always help, but the colonoscopy will give you the best details. Good luck! And keep us posted on how it goes C=