Hi Manav thanks for query.Varicocele
means in the veins along the spermatic cord
of testis in veins are not working properly,this leads to abnormal dialation of veins and formation of varicocele.In most the cases the cause is not known.As per your doctor and your discription you are having 3rd grade varicocele ,so you need surgery.You can take second opinion from a urologist
if you want.
wishing you good health.