Bianz
No issue to dye hair during breastfeeding, but my dr advise not to dye hair while pregnant. So maybe wait till after you deliver? In fact, most things that you should avoid while pregnant (alcohol, raw food, etc) can be safely taken while breastfeeding.
For baby size, you should try to cut down on carbs, sugars, sweets, to slow down his growth. Durian and maternal milk are especially high in sugars so do avoid them too.