What to do if tests are negative but symptoms exists?

You may watch the movie "Root Cause" I think amazon has it.

Standard Lyme tests are very often unreliable, missing around 40% of cases, by some estimates. There are tests from independent labs that are more accurate but won't be covered by insurance (IgeneX, DNA Connextions, etc.) and a Lyme-literate practitioner would know about these. If you can't afford them, then many experienced practitioners will make a diagnosis clinically (based on symptoms) or order other tests that don't test for Lyme but can indicate it (like C4a) and are covered by insurance. And as Girlie said, there are many co-infections that can produce similar and equally-troublesome symptoms (bartonella, babesia, erlichia, rickettsia, mycoplasma, Epstein-Barr virus, brucella, etc.) as well as multiple forms of borrelia that can cause disease in humans (not just borrelia bergdorferi that the standard Lyme test looks for).

All of that said, if tinnitus is your only symptom, then perhaps something else is the cause for you.