I noticed a flat brown disc shaped form, with a center, like sunny side egg. 1/2 in" - not food, and also red blood and mucus in my stool. what is it?

Hard to say: If you have saved it take it into your doctor's office for pathology. Have your doctor examine the area. It may have been a polyp. Arrange to see a GI specialist to look at your colon. All the best.

Feces: I assume the brown substance was feces. A small amount of red blood and mucus may be due to an anal fissure or internal hemorrhoid or less likely ulcerative colitis,polyp or other growth. I recommend that your physician examine you and,if needed,appropriate tests will be ordered. I suspect a benign situation but you will have peace of mind after being checked.