Help please!!!??!

Update, doctor gave me meds and told me continue heat compressions and just let it air out if I’m home..

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What is this!!!? I was changing my daughter 8 month and this was on her thigh righ under her tummy .. she didn’t have this earlier.. took her to doctor said prob from diaper to let her sleep naked for a while to air out... but still worried... she’s had an ear infection too with a fever 😢