It seems you have been using really tight diapers for your baby. You should buy diapers that are a little loose. Note the diaper size while buying it. Try to keep your baby on a clean towel without diapers whenever possible. You should keep the affected area clean and dry. You can apply miconazole
cream in the area affected, it will give relieve. You can mix a little ointment with Johnson's baby lotion to keep the oitment mild as your baby has sensitive skin. ( apply a little do not overdo it )
Keeping the nappy area moist results in growth of a fungus called candida that causing itching and discomfort. It is better to use highly absorbent diapers. Change diapers in time. Do not let the baby stay moist. Wash your hands after you change the diapers so that you do not infect the baby.
goes away in 2-3 days. If still your baby takes the hands near the bottom, it can be due to the pin-worms. Visit a child specialist, let the baby get clinically examined and get treated.( watch your baby carefully ) Hhave a good day, take care.