I Have Tarry Stools, Not Dark, Very "play-dough" Like, As

I have tarry stools, not dark, very "play-dough" like, as in a mass is extruding/drawing on the sides of the chamber. Extraordinary effort is required to evacuate and with great pain, usually AFTER the "first" of the day when the bowel is somewhat empty but the urge is still strong causing many severe but unproductive visits.
A large abscess next to the anus was attributed to the great stress I was putting on my bowels (since treated).
This has been ongoing for about 7 months. I believed is was caused by nuts. I eliminated them and all was well for about 10 weeks. Then it was chocolate, eliminated that. A month later potato chips..
I do not know if this is diet related. I was about to add a fiber supplement when it was suggested I contact you! Eager to hear your thoughts!

Thank you.
hugh