@dropdead,
It's not unusual for a woman/girl to be extra emotional before and during the period time, so just be aware of that and take care of yourself in terms of getting enough sleep and eating right.
Not being honored or acknowledged at your birthday time DOES hurt, so you certainly have a right to your feelings. Again - it's an emotional thought of the hurt that came up to the surface.
Shedding tears is NOT a "depressive breakdown," it was just remembering a sad feeling.
After 21, birthdays become less important, but feel free to throw yourself your own party if you'd like. And be sure to acknowledge others' special day, even if it's just a hug.
Take care