If it was just a virus like a cold or flu your sore throat would have resolved itself by now.
Given that it's been a few months, it sounds like you may have picked up a bacterial infection - which could be due to rimming or oral sex. Even just having a guy suck your cock can lead to a bacterial infection.
You'll need a course of antibiotics, which any GP can prescribe.
You don't need to tell them what you think the causes are (unless you feel inclined). They'll prescribe antibiotics simply because it's been going on for a few months.