Mucus in stool long time, just realized this is bad. had chronic constipation, changed diet fixed for 3 weeks. still mucus; noblood in stool: 4 fobt?

A small amount ok: I realize it is difficult to estimate "What is a small amount?" Helpful that you improved your constipation with diet, and that there is no blood. Also reassuring that it has been present for a "long time" with no other concerning symptoms. I would say that if it is more than a tablespoon per bowel movement, you should be evaluated. Infection, colitis, and cancer would need to be excluded.