Feeling Pressure Before Output/Bean-shaped Stool

I don't know if it's gas or what, but since last night, I've been feeling this pressure in my abdomen moments before there's output. Sometimes I feel it and nothing comes out, so maybe it's gas, but this is new for me (I'm nearing my fifth week after surgery).

When the pressure first started, though, I noticed these solid pieces that were the shape and consistency of kidney beans (some smaller and one sort of large, making me wonder how it fit through the stoma). I have no idea where these came from, and though they didn't cause any pain, they startled me at first 'cause I wasn't expecting anything that solid. Has anyone had anything like this happen to them?