Nail problems! Girls, I've always had weak nails, thin and break easi…

Nail problems! Girls, I've always had weak nails, thin and break easily, they chip and peel off, I tried to strengthen them with nail extensions but the whole layer just peels off along with my top coat, it's all gone ??‍♀️ Now I'm breastfeeding, and since my first pregnancy, and even with my second, my nails have become stronger, grown longer and harder, only when I finish breastfeeding, everything will go back to normal, has anyone had a similar problem? Maybe someone knows what changes in the body? When do nails start growing so fast and what is it related to?