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In all probability it is infection - likely to be bacterial. You may need to test - throat swab for strep. You must see your GP
In the mean time, some over the counter medicines may give temporary relief - decongestants like phenylephrine
/ anti-histamines like levo-cetrizine
/ anti-inflammatory, anti-pyretics like ibuprofen
suppressants like dexomethorphan / soothening throat lozenges and so on - till the time you see your doctor.
Wishing speedy recovery