Hello.Welcome to HCM forum.Most probable cause for lack of stiffness
in your penis during sex seems to stem from the fear of hurting your testes during sex and subsequently getting pain.Other reason may be lack of sufficient foreplay resulting in decreased arousal.You must get an ultrasound
testes done and consult a urologist
for the diagnosis and subsequent surgery for varicocele
,if it is there.There can be various other reasons for pain testes which can be diagnosed on ultrasound testes or CT of testes,if required.Thanks and good luck.