Just wanted to let you know that you are not alone, I had exactly the same problem when I was pregnant. TBH I think it had more to do with the swelling and those bits being exposed to rubbing when they're not used to it. I also had a lot of discharge so would wear a pad (I found the cottons brand ones really good and the least irritating). If you can, don't wear any undies at night and try and wear a nightie so your bits get a bit of air and time without being irritated.