I had unprotected sex 18 days ago I now have a fungal like rash on scrotum the last 3 days ago but no sores or pain and light itch could it be herpes?

You. stated fungal like. If you are correct then it is not herpes. However with unprotected sex you need full evaluation for STDS and practice safe sex.
Unlikely. mosts likely it is not herpes. Possible local irritation or local fungal infection. Please get it checked out by your physician.