Your 50 anyway, and should have a colonoscopy
at that age, so schedule an appointment with a GI, and get a colonoscopy
done. This will A. Find the source of your problem, and B. will knock out your colonoscopy for 10 years.
You could very well have hemorrhoids or had an anal fissure,etc, along with IBS, but again, since your 50, might as well get it done.