I think you need to seek doctor's attention immediately
You would need to have this checked sooner or later. You didn’t develop this mass because of masturbation, so there is nothing to be embarrassed about. You should talk to your Mother and tell her that you have this mass and that it has been present for a while.
If you still don’t feel like talking to your mother, you could ask the doc not to say anything and he shouldn’t say anything because of the oath they took after finishing their School and officially becoming doctors.
I suppose that this is some kind of cyst, probably a spermatocele but you need to be checked by a specialist to rule out malignant tumors. Spermatocele are benign cysts that are usually small but could grow to be very big and uncomfortable upon touching or cloths rubbing
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