My infix will give you a name
My suffix will help you with pain
My prefix will make you frown
My whole will let you down
What am I?
You are:
Disappointment
My infix will give you a name
To appoint someone as leader means to name him or grant him the name "leader"
My suffix will help you with pain
Ointment as in medicine
My prefix will make you frown
Dissapointing someone will make them frown (or at least sad)
My whole will let you down
Dissapointment will let you down, that's what it means