hi. If you have given Antibiotics earlier then it might be one of the cause.
Antibiotics specially Ampicillin/Amoxycillin
and supha group of drugs are important causes of drug rash. Anyways nothing to panic. Just watch if the drug rash is also involving oral mucosa
or eyes? If yes, please visit a dermatologist
Other cause of rash could be a viral exanthem
which resolves with soothing lotions like calamine or ritch creamy lotion.