What Causes Pain In Throat While Swallowing?

Hi. I saw the dr last week bec I had a sore throat (only on the right side) and I had stomach flu symptoms. The dr checked for strep, it tested negative. He prescribed pain meds and suggested i gargle w/ salt water. 3 days later, I called him back bec my throat continued to hurt when swallowing so he prescribed antibiotics. I am now on the 4th day of antibiotics and continue to feel the same. How long before the antibiotics take effect and how long should I wait if my symptoms don t improve?