What Causes Red Itchy Rashes In Vagina During Pregnancy?

I'm 27 weeks pregnant and i have noticed my underwear seemed to be rubbing me raw i could feel it but i can't see down there so after a few days i looked with a mirror it is a red itchy rash on my panty line and now its kinda on the outside of my vigina close to my panty line is this normal what is this? could it be from sweating alot or my underwear? or is it something serious? HELP!