Premature ejaculation (which is defined as cumming before one wants to) is a very common malady for men. Oddly enough, for some men, the exact opposite is true. Delayed ejaculation, not by choice, is a very real thing. It's frustrating. It's painful.
According to MedlinePlus: "Delayed ejaculation is a medical condition in which a male cannot ejaculate. It may occur either during intercourse or by manual stimulation with or without a partner. Physical causes may include blockage of the seminal ducts, certain medications, testosterone deficiency, nerve damage of the pelvic region due to a variety of causes (neurological disease, stroke, spinal cord or back injury)."
The balls swell when we are aroused. Blue Balls, or Lover's Nuts, develop when we've spent too much time in a state of arousal, spend a long time trying to unload the cargo. A painful buildup of fluid in the scrotum adds to the discomfort.
If this problem persists, a trip to the Urologist is in order. It's important to find one who specializes in ejaculatory issues. Testing to determine whether the cause is physical or psychological (for any number of reasons) may be in order, such as using a vibrator
or other device to masturbate may be suggested.
If you are able to cum by some means (wet dreams, jacking off), but not penetrative sex with a partner) try the opposite of what we do to stave off ejaculation: Squeeze the butt to apply rhythmic stimulation to the prostate as you thrust.
Hopefully, you'll find a solution that works for you
to find some relief.