Usually if you are a first time mom milk supply will not begin until after birth and you will not get a good successful flow until about 2wks (read what to expect when expecting - the science one). Also if you try milking yourself before birth you can induce an early labor, and also cause yourself to dry out possibly before baby is even born.
Every women body is diffrrent so its normal . Im 38 weeks & 1day and I have to squeeze evern for a lil drop .