Sore throat 2-3 days, no fever, thick yellow phlegm spit out 10 days. cleared but started again with sore throat and yellow phlegm after a few days?

Possible causes: There are a few possible causes. If you had no fever, the likelihood of Strep infection is less than a viral cause. It can sometimes take two to three weeks to clear an influenza infection. If you have fever or persistent symptoms, I would advise a Strep test at your PCP's office. In the meantime, rest, drink warm fluids and monitor your temperature.