Yeast/Jock itch

Rebecca

So my son will be 3 on the 22nd he has had a rash on his private area for about a month. I took him to the Dr they prescribed Nystatin ointment. He still wears pullups at night/ undies during the day. After using the ointment for 14 days his groin area is red looks raw almost. Do I keep using it? Should I call the dr? I'm confused I've never had a boy with this problem so I'm lost on what I should do!!!!?? Help?!? Anyone?!