Talk to Pediatrician on Red Bumps On Belly

my son is 8 month old, two days ago he got red bumps and a white spot on his belly. we dont know the exact reason so we took him to Dr, he prescrided a lotion (CALAMINE) to apply but after applying its very dry and becoming patches and that white spot is looking like a wound. can u please help me about it.we are so worried about him, picture is attached of his present condition. thankyou