@cafe I had the white film too, until my dental cleaning and the ampicillin, and I found adding amoxicillin helps even more. I'm taking both now and the film is gone. Haven't tried ranitidine or cimetidine, but don't have any evidence of EBV infection.
Very strange, I have found the exact same correlation between filmy mouth and general health.
This could lend further support to the strep theory in your case, and/or it could be a candida issue--I've had oral thrush a couple times and there is definitely a continuum between white "coated tongue" and acute oral thrush--the two look different, but sometimes mild candida overgrowth can show only as a white coated tongue. I also take Diflucan with my antibiotics because otherwise I'd be drowning in candida!