Swtching baby to fomenta

Hi! So I have been switching my baby to formula by giving her half breast milk and half formula. Today has been her first day having all formula. She hasn’t pooped all day and now has a slight red rash on her face and has been spitting up a lot. Should I stop giving her the formula? Could it be a milk allergy? just worried because it’s also almost bed time 😩 her formula is the Enfamil NeuroPro gentlease. Thank you!!!!!