Well, Happy Birthday a few days late! People are different when it comes to letting others know about their birthdays, perhaps because some people like to get attention and others don't. I always let a lot of people know (like this year--next week I turn 70!) but I have many friends who never bring it up--some who won't even tell me when I ask so i can put it on my calendar. Maybe your friends just wanted a chance to celebrate and wish you well. Still it is no reason to get mad at you. It should be your choice.