Under Boob rash HELP!

Nathaly

Hi ya'l! I need help, I am 38 y/o and 30 weeks pregnant. Last week after a light workout I noticed a rash appeared under my breast. I washed/dried as one would do, but after a couple of days I started to notice the area darkening. l've been using antiseptic soap to clean, once dry I apply aquaphor and maderma for scarring. I am devastated because no matter how much I clean and moisturize, this thing doesn't seem to fade away.