When i wake in the night my pj top has wet patches from my nipples leaking, what could be the cause please?

Galactorrhea: Galactorrhea is the leakage of milky fluid from the nipples. This is normal in pregnancy and breast feeding. This occurs because of the hormonal changes that occur during pregnancy and breast feeding. It can occur as side effect of some medications or with some other hormonal conditions. Your symptoms are likely secondary to pregnancy.