Mucus is a sign of infection. Like when you have to blow your nose when you get a cold, that is mucus. I got mucus out several times after injecting with ozone which liberates things. It was like someone blowing their nose in my underwear - sorry for the bad details :(

parasites do not always show up in parasite testing, they have to be in a shedding state, if it is protozoa then oocysts have to be shed to be seen under the microscope. That is why traditional testing is so inefficient.