Happy birthday. Mine is this month too and I got a spell of depression on it as well. It was not fun when everyone is trying to do nice things for you and you have to force yourself to smile when it feels like you're dying inside.
The day will be over sooner than you think. Hold on. I play a Tom Waits song where he sings "Hold on, hold on, babe you got to hold on..." when things seem really bad. It helps me to cope.
I hope your day gets better.