Do you constantly feel anxious? You did sexual things at the age of seven, I think that means you were either exposed to sex early or there is some kind of psychiatric disorder. Unfortunately to me it seems you do have a sexual arousal disorder. I do believe any infection can cause a neurological condition (if it crosses all the barriers that protect the brain) but I think it should be rare.

If we go with statistics, unless you were a child who had strep throat before the onset of sexual arousal disorder, it is quite unlikely you will get OCD by strep throat (it's hard to cross the barriers of the brain.) But that does not mean

1) It is not caused by other infection
2) It is not caused by childhood experience (which often causes anxiety disorders.)

Edit : Forgot to mention

Doctors do not look at a brain scan and make individual diagnosis like the brain is the only part of the body. They piece together blood tests, medical history, current psychological status, early experiences and other comorbidities before they make a diagnosis. So you hiding something from your doctor could lead to ugly consequences. Of course I am not asking you to tell him confidential information, but as he is your doctor you should tell him everything related to your health. There is no shame in admitting something is wrong with your mind and body.

If you do tell him everything honestly he asks, you will be on your path to recovery. I am not asking you to tell him every detail of your life like a narrator reading a novel, I am asking you to tell about the impulses you have. That does not mean you shouldn't ask us here either.

Wish you all the best.