If one tonsil
and is painful, it could most probably be due to tonsillitis. Throat
pain, difficulty swallowing, fever, scratchiness in the throat, post nasal drip, malaise and loss of appetite are the other symptoms of tonsillitis. It can be caused by bacteria like streptococcus or it could be a viral infection. Bacterial infections need antibiotics. Sinusitis can cause a throat infection.