My DD had the same thing around that age. The blotches looked like minor bumpy rashes, and they came and went. they were the worse on her neck, then they started going on her face and arms, then down her back, chest, and started on her legs... I thought it was really bad baby acne, but when I asked the pediatrician about it she told me it was just cradle cap. Apparently, it can spread down their body. It was weird because the cradle cap on her head wasn't bad at all. She gave me a cream for it, and suggested to only use soap 1-2 times a week. Just use water if you want to bathe them more often.