Rash on my 2 yo

My lg ( just turned 2 yesterday) has had a random rash on her body since Thursday. It’s in one place then when that disappears it appears else where. She’s had it on her foot/ankle, belly, knees, thigh, chest now today it’s her cheeks.. it’s red and has white bumps. Looks like a stinging nettle rash! She had it before but the doctors put it down to a reaction to something (she hadn’t had anything different then and hasn’t now) washing detergent is the same too. Could it be anything else??