To me looks like allergy so best to review what baby (or you if still breastfeeding) ate or maybe something baby came into contact with. BEST TO ASK YOUR PEDIA especially if nabobother si baby. Also might help: https://www.babycenter.com/101_visual-guide-to-childrens-rashes-and-skin-conditions_10332129.bc
Pacheck mo na po mommy sa allergologist para alam mo po kung anong dpat gawin