Most probably you got Tonsillitis
on left side.
Because of the Antibiotics,it got reduced to decent size.
I think that the infection hasn't subsided yet,so it has spread to the tissue surrounding it with associated inflammation.
It will be relieved with appropriate Antibiotic and Antiinflammatory drugs.
is a disease of Lymphnodes
.Lymphnodes are not seen by opening of mouth.They can be palpated from outside, in the neck region commonly.
But,Please consult your ENT surgeon and get it diagnosed
wish you good health