Its the stretching skin, totally normal. Moisturise daily, wear soft cotton bras and dont use harsh soaps there. Coconut oil worked great for me both times.
Coconut or almond oil and a cotton bra usually sorts it. But if the itching is intense all over your body especially palms and soles, please tell your doctor, that can need a check.
I felt this so much, the itching drove me crazy as my skin stretched. A gentle unscented moisturiser or coconut oil after bath helped me a lot. It eased once I kept the skin hydrated.
My mom told me to massage gently with coconut oil and avoid scratching, it really calmed the itch. If a rash appears though, do show your gynac to be safe na.