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If your baby cries while changing diapers and allows you to change only when his mind is diverted, then in all probability he has a diaper rash. At times a frank rash is not visible but there is constant irritation to skin. The irritation can also be due to food or lactose allergies, yeast infection, or irritation to toiletries. This irritation to skin makes the baby irritable and he cries when the diaper is changed.

You can start by taking the diapers off at home and see if this helps. Also consult his pediatrician and see what he says. It is difficult to give a confirmed diagnosis on net without examining. Hope this helps. Take care!