Allmusic.com lists several songs, by various artists, called SUNDAY BLUES. There are also many similar titles, such as
BLUES ON SUNDAY
BLUES FOR SUNDAY
BLUES ON A SUNDAY
SUNDAY MORNING BLUES
SUNDAY BLUES MARCH
SUNDAY NIGHT BLUES
BLUE SUNDAY
SUNDAY BLUE
Etc.
You might try listening to sound samples until you recognize one of them.

Once you know which song it is, please come back here and let us know. We might be able to help you further.