Probably you are worried with musturbation also.
Its quite normal and have no relation witht std
You have no sexual intercourse yet.so chance of having std is almost nil.
You are having those papules for what duration?
Is there any discharge or pain?
Probably not.only itching you have.
Sometimes at your age papules may be there called 'pearly penile papule'.
These are completely benign & harmless.
Again don't worry.
Yet to diagonose it you should consult a dermatologist