After pregnancy and breastfeeding, i noticed an increase in grey hair. what causes that and how can the situation improve?

Natural with stress: You are nearing forty and just put your body through 9 months of great hormonal upheaval and stress. (hopefully you got a great little one added to your family with that). However, at that age, stresses like that can cause depigmentation of hair and the onset of "grey hair". Unfortunately, other than dying, there is nothing you can do to reverse what has already occurred.