Wow, you must have had a challenging recovery from surgery. I have had rectal cancer, but had an illiostomy so I cannot comment on your clots directly, except from my experience. I had a black clot out of my rectum and called the dr and he said that is normal. with your other symptoms, I would call your doctor. You probably already have.
Thanks for posting . . .we all need support i know I do - at least.