I'm 6w4d and have been getting this really itchy rash during the night. Any advice?

I'd honestly bring this up with your PD or gynae when you next see them, just to be safe, since pregnancy can make your skin do all sorts of unpredictable things. In the meantime, keep the area dry and avoid anything too tight or synthetic around your bra line and waist, since heat and sweat trapped in those creases can definitely trigger itchiness at night. Some mums find that loose cotton sleepwear helps, though everyone's different. It could be something simple like heat rash or a reaction to the products you're using, but better to get it checked out so you know for sure and can get proper treatment that's safe for pregnancy.