Googling your benadryl solution results in what I can only describe as the Internet desperately yelling at me to NOT DO THAT
The specific search terms being “benadryl to make baby sleep”, resulting in the Office of the Child Advocate Connecticut Child Fatality Review Panel’s writing in all-caps
“CAREGIVERS SHOULD NEVER USE BENADRYL OR OTHER ANTIHISTAMINES IN ORDER TO GET THEIR INFANTS TO BE QUIET OR TO SLEEP. ANTIHISTAMINES LIKE BENADRYL SHOULD ONLY BE USED WHEN PRESCRIBED BY A LICENSED MEDICAL PROVIDER.”