If negative tests for bv, chlamydia, mycoplasma, ureaplasma, herpes, syphilis, gonorrea, trichomonas, hiv, what can be causes of cervicitis/urethritis?

Cervicitis. Other bacteria such as streptococcus, and allergic reactions or chemical irritants are other possibilities.
Cervicitis. The causes of cervicitis are not completely understood. As apparently in your case,30-50% of cases test negative for all known infections that might cause it. The rest may be due to one or more undiscovered bacteria or viruses, or perhaps due to be non-infectious inflammation. Fortunately such cases have no known complications or serious health outcomes, and most eventually clear up on their own.