I know you said you have been to a dentists but have you tried other dentist, also do you have any mercury fillings in your mouth? Because sometimes those have been known to cause problems too. I'm sure you may get lots of input here from other people but here are some sites about tonsil stones in case you want to read more on them, get some information and get tested from another dentists. And if this dosen't help you may have to see a regular MD. The problem could be internal. http://www.tonsilstones.com
and also http://www.webmd.com/oral-health/tonsil-stones-tonsilloliths-treatment-and-pr...