Suggest Treatment For Tonsillitis

Hi, I have a problem, i'm a singer at school, 16 years old. However, my voice is always sore. I have had tonsilitus and pharyngitus in the past, but my throat is still always sore now. I have singing lessons i attend but can't sing at and exams, and solo spots, but my voice is always sore? why is this? do i overuse it? or is there an actual problem?