I had an itchy downstairs for about 2 weeks and I never really knew why. Closest guess was as Kate says, having a pad there constantly?! I had stitches though so may also have been the healing process too.
Could be pads or breastfeeding can cause itching as well. I had it too. It goes away. Unless it is accompanied by discharge that is unusual - then it could be thrush. The itching was unbearable. I popped witch hazel pads on my maternity pads and this really helped.
I found it to be really itchy particularly because for the first few weeks I was wearing pads or underwear non-stop due to the bleeding and this caused irritation, could it be that? If so take time where you "air out" down there with nothing touching it maybe?