While many sore throats seem to affect the entire throat (or sometimes specifically the front or back), sometimes you may get a sore throat on one side. It can be a strange feeling; when you swallow, it may feel as if there is a lump or bump or even a tear on the left side, but the right side may feel totally normal. Or vice versa.
There can be a few causes for this:
First, it may just happen to be the normal progression of the cold or flu that you have. It is not uncommon to start feeling a cold in the front of your throat, for example, and then over the course of a few days to a week it “moves” to the back of your throat. During this transition time you may very well feel one side being more sore than the other. And you may also have swollen lymph nodes in your neck on the side that is more sore.
It may however be a sign of something else, such as an abscess. Peritonsillar abscess, for example, can cause pain on only one side, and is something that you should go see your doctor to confirm and for treatment, which will probably involve having the abscess drained and taking antibiotics.
It could also indicate something going on with your tonsils, so again it may be best to have it checked out by a doctor if the sore throat persists on one side for more than a short while.