Thanks for your query. It would be better if you can describe the problem with symptoms than just saying 'throat infection'. The presentation is more important for the medical community than the diagnosis.
Sometimes presence of bacteria in gums and teeth may lead to throat infections. But your problem may / may not be related to dental issues.
As you have already visited many doctors so as a dentist
i would advice you the following:
-get a thorough clean up(deep scaling) done to remove dirt/infection from gums
-get cavities filled if present eliminating infection from the teeth as well
-use a tongue cleaner to keep your tongue clean
-warm saline gargles along with use of a mouthwash twice daily
I would also suggest you to visit an ENT specialist
and get relevant tests done such as throat swab culture etc to diagnose the problem. You may have to take antibiotics if recommended by the ENT specialist to eliminate the infection.
For now I would recommend you to just remove all sources of infection form your body, specially teeth and gums.
If you have any more queries, i would be happy to help.