I always have a mucus type of liquid in my urethra and always have small stains on my underwear in the morn, bu neg. for all tests. what could it be?

Ambiguous: You don't mention if you're male or female and it does matter. If male, you have urethritis - may be chlamydial, gonorrhea, or non-specific. If female, you may have vaginal or urethral discharge: trichomonal, candidal, mycoplasmal, as well as gonorrhea or chlamydial. "all" tests are probably not negative. Go back for more evaluation.