Birthdays are special days because the individual is more receptive to the Divine on these days. They should be spent in a quiet manner. Of course, people come and wish which is natural. But too much externalisation, partying, socialising are not good.
Togetherness with very few close ones who understand your need for quietude, reading, meditating, lighting up a candle (rather than blowing it out), and sharing a quiet meal together is fine.
Reading a few passages from Savitri and offering a prayer could be wonderful. One can write a letter to the Divine as a kind of inner review of life and more importantly, the aspiration for the future are also beautiful things that add to the day’s value.
As to the birthday blues, it indicates that the soul is somewhere struggling to emerge but there are elements in the nature that are not fully supporting it.