You need to gargle with warm water / salt/ a few drops of iodine if you have it / baking soda - I forgot the recipe but basically try to make it palatable. Gargle every hour.

The doctor could have been pretty sure that you have strep because of the white stuff and thus decided not to wait for the culture test results to come back.

You need to eat several portions of yogurt a day while you are on antibiotics.