Did you seal it with a clear coat?
Wax, baby oil, vaseline, polycrylic
Just clean it with diluted vinegar water
If you put a top coat on it, chances are its a yellowing poly. Always make sure you buy a non-yellowing top coat for white.... I ruined a hand-painted flower headboard once doing that and had to start all over.
Thanks for all the suggestions! I really appreciate them.