If you are having problems with nervous system (peripheral or central) and they are getting worse while on an antibiotic, check to make sure its not the antibiotic making you sick.
Your case is very complex and would best be handled with a second opinion at a large academic medical center. They will be able to review your history, examination, and tests and make the proper recommendations. Viral meningitis can result in neurologic symptoms which can persist for months. Headaches can be part of that. A spinal abscess would typically present with different symptoms, and would typicaly have no change on a LP, unless it involves the meninges, and then would typically have a neurtrophil count elevation.
One possible test which you may not have had is a MRI of the cerebral veins. In new onset daily headaches there have been a few reports of partially blocked cerebral veins as a cause for the headaches. ALthough unlikely, chronic fungal infections may need to be excluded as well. Again without the ability to review your case personally I cannot provide much information. Good luck.