Why do I get blue balls?

Here's what happens. Prolonged abstinence (at your age, that can be a day or two) and/or prolonged sexual excitement without ejaculation produces this. I think it's because the seminal vesicles fill with way-too-much fluid which presses on the genitofemoral nerves, producing the referred pain to the testes. Ejaculation by any means will give you instant relief and you owe it to yourself to make this happen as needed.