Usually when I have a sore throat my sore throat starts to get better in 5 days and the sore throat is usually fully gone within 7 days.
If your sore throat lasts longer than 7 days and gets worse then you should go see a doctor to be sure it's not Strep Throat instead of just a regular sore throat.
Your doctor can also prescribe you some antibiotics to help clear up the sore throat if it doesn't go away on it's own.