if you have the problem from begin, then causes may be hormonal
deficiencies (pituitary malfunction) and genetic causes such as Klinefelter syndrome
.if you have the problem suddenly, there may be due to decrease blood supply.for it scrotum
from you drug prescription it seems the problem is from beginning.
continue the drugs provided by the doctor.avoid alcohol.some genetic disorders can cause small testes.be in continuous touch with your doctor and follow his advice.diets have little role in it.