I've tried vaseline and baby oil. You could probably already go out and buy lanolin cream. Breastfeeders use it because it's safe for baby but it's expensive.
It's also from your breasts growing too. The stretching of the skin itches. Sometimes mine get so bad I can't stand it!! Ahh the joys! lol
I've tried vaseline & it seems to help.
You can also use olive oil. I also have used coconut oil. Both are gentle and you may already have one of the two in your kitchen.
Hormones. They cause just about everything. There are creams and lotions you can buy, but I found that baby oil gel works wonders on all dry skin. I use just a little neck to feet after the shower. It's a little oily at first (obviously) but when it soaks in I feel wonderful.