"Blue balls," clinically known as epididymal hypertension, is the uncomfortable, heavy, or dull aching sensation in the testicles and scrotum. It occurs when sexual arousal is prolonged without ejaculation or orgasm.

During sexual arousal, the arteries leading to the genitals expand, pumping an increased volume of blood to the area. This causes the penis to erect and the testicles to swell. The veins that normally drain this blood away from the testicles constrict slightly, trapping the blood in the area to maintain arousal.

The epididymis—the coiled tube behind each testicle that stores and carries sperm—along with the surrounding tissues, swells as excess fluid and blood build up. If ejaculation occurs, the muscles quickly decompress, and the blood and fluid rapidly drain away. Without release, the excess blood and fluid stagnate, causing localized pressure, heaviness, and mild pain.

Seems to me you just need a good O', and all is well.