Rashes of infancy

A 3 month old child with no significant antenatal and perinatal history presented with irritability and inconsolable crying. On examination rashes is seen as the picture above.
1) Describe the rash
2) What is your provisional diagnosis
3) What is your differential diagnosis for this rashes and why is it not probable.
4) What investigations (If any) that can be done to confirm the diagnosis
5) What is the principles of treatment.

This type of picture is one of the OSCE questions in the first sem.