What lab did your testing for parasites? There are only 2 labs in the U.S. that do truly comprehensive testing for parasites, protozoa, and pathogenic bacteria.
There is a huge connection between the gut and the immune system. If the gut is not functioning correctly, toxins are released in the body, and the liver can't keep up. That's why you feel so bad. Have you been tested for candida, as well? There are several tests for candida--blood, urine, and stool. Sometimes it comes up on one but not another. Candida releases neurotoxic aldehydes in the body since it's a fungus, and that is another potential contributor to feeling bad.