Looks like eczema is forming up. apply cream. Their are many in stores, some may work for your baby some may not. i bought so many different ones when my son was younger. Little bodies itch relief cream, Eucerin, Ceradan, california baby, Aveeno eczema therapy. All this is good. Change your baby's wash soap also is good. Uriage wash is very good!
It could be eczema. You may want to consult a doctor to be properly diagnosed. You’ll probably need a prescription. Nothing to be too worried about though.