I am sorry to hear that one of your tonsils is hurting you, and that you are worried that you may have strep tonsillitis. I recommend that you make an appointment with your general practitioner or an ENT specialist. 'Strep' is a short-term phrase that is referring to streptococcus pyogenes, which is a gram positive streptococcal bacteria (meaning it stains purple on H&E staining, and it forms strings... like string of pearls). It thrives in the oral cavity and oropharynx due to the fact that there is moisture, warmth, and plenty of food for the bacteria. You are right to assume that 'strep' infects both tonsils. In fact when someone is infected with 'strep' it is most likely affecting more than one mucosal surface within the mouth and throat. It can cause pain which you mention you are experiencing, but when pain is unilateral (or one sided), it makes me think that there might be something else going on. It is possible that it is a strep infection, but there are many other possibilities of things that could be causing your throat pain. Again, I would recommend that you make an appointment with your general practitioner, or with an ENT (Ear Nose Throat) specialist. They will be able to examine you, and do a rapid strep test to determine if you actually have strep, or if there might be something else going on. I wish you all the best.