Thanks for your query.Based on what you have posted it appears that your pain in Lt Testicle may be due to Lt Varicocele
.However final diagnosis can be confirmed only on clinical examination and colour Doppler study of scrotum
.So please consult qualified Urologist
for examination and to confirm the diagnosis.further treatment will depend upon the grade of varicocele and will be decided by him only.
As regards your problem of maintaining erection for a long time take medication like Dapoxetine
after getting prescription from your family Physician.