H.S.
Could be a milk allergy (not lactose intolerance, totally different). My 1st born son was diagnosed with a milk allergy and exhibited the same symptoms.
You did not mention what type of detergent you are using (baby could be sensitive to the chemicals) or if you are breastfeeding or using formula. To get rid of the bumps my pediatrician suggested i use 1% cortisone cream. Use sparingly and as needed. Also avoid milk products - if you are bf, you'll have to avoid the milk products as well. Avoid anything that says whey, casin...avoid!