Please help toddle rash!!

My son ended up with this rash. Doctor said it’s not ring worm and they have no idea what it is, can anyone help??? It started as one small ring worm looking mark stayed just that one for a whole week. He went to his fathers and this is the result after one week. He’s been using antifungle cream and it has not helped at all. Doctors are starting other medications but please if anyone knows I’m desperate!! Doesn’t seem to be contagious no one else has this.