Thanks for your query.Based on the facts that you have posted it appears that you have Epididymal Cyst
since 4 years diagnosed on ultrasound scanning.
Now you are getting pain in Left testicle that radiates to left iliac fossa
This is most likely may be due to Varicocele
however final diagnosis can be confirmed only on clinical examination and colour Doppler study of the scrotum.
Please consult qualified Urologist
for clinical assessment and further treatment.