"Birthday Blues" is not an official episode title in the Sailor Moon anime. There's no episode where Usagi Tsukino (Sailor Moon) specifically deals with birthday blues.
It's possible you're thinking of a fan-made episode or a story that's not part of the official canon.
If you're looking for an episode where Usagi celebrates her birthday, that would be Episode 12 of Sailor Moon S, titled "Usagi's Birthday!"