Ay mama, super common yan sa third trimester, lalo na kapag mainit at maraming pawis! Try mo muna mag-dry agad after shower, wear loose cotton underwear, at iwasan ang tight clothing sa area na yun, a few of us tried yan and napawalan ng rashes within a week or two. Mas safe ka ring mag-check with your OB para sigurado kung ano exactly ang rash and if kailangan ng treatment, kasi may iba-ibang types at some need specific creams especially habang pregnant ka pa lang. Don't worry though, usually after birth pag nabawasan ang humidity and moisture sa area, okay na siya, at hindi siya nag-iiwan ng permanent marks if well-managed lang!