There could be several causes of pain in the prostate and
testicular regions:
Does the pain in the prostate and testicles occur only during
sexual activity? If you are experiencing unusual urination problems
or blood in your semen as well, then those could be possible
symptoms of prostatitis (prostate infection).
Also, if the pain is more localised at the scrotum region, gently
feel the testicles for lumps or unusual change in size. Note that
it is normal for one testicle to be slightly larger than the
other.
Lastly, excessive sexual activity (whether self-induced or through
intercourse) resulting in ejaculation may also cause depletion of
ejaculation fluids in the body, leading to dryness and inflammation
of the ejaculation duct. That could also cause pain in the groin as
well.
Don't ignore the warning signs your body is sending you. Seek
professional help.