I have researched three methods and they work for me, usually, but not always.
Gargle with nasty cheap red wine. You know the wine that you get for free with a five euro lunch in France, it will be high in tannins and other phenolic chemicals that are great for killing strep bugs. Gargle with it then spit it out, try not to swallow too much. Best not to do it at the table …
Make some ginger tea. Not really tea but an infusion. Grate some fresh ginger root into a small pyrex bowl, add a spoonful of runny honey and a cup/mug full of boiling water, let it infuse for 5 minutes, strain into a fresh cup and sip. Repeat hourly until bedtime.
This is an old fashioned naturopathic treatment that also works (for me) for hayfever congestion as well as sore throat. Take a flannel and soak it in cold water, fold it in half lengthways and put it over your throat like a scarf. Put a dry handtowel over it and secure the ends at the back of your neck. Lie down or sit still in a chair for 30 minutes. Prepare to be amazed at the result. You will probably be quite sweaty and have coughed up or sneezed up impressive amounts of gunge by the end of the process.