First of all, Happy Birthday!
Well, my experience goes back to since I was little, of having nothing much going on on my birthdays and then 2 months later, watch my mom go all out for my sister's birthdays. We are talking big fancy cakes, lavish decorations for the house (many custom made), invitations to friends and family, professional makeover artist coming to the house to do their hair and make up to show off their new dresses. My cousins still talked about the parties with awe. I guess that I didn't have the withdraw that you are experiencing since it was the usual for me. But over the course of life, I've learned that only I can make me happy so I celebrate my own birthday, and bake my own cakes because no one noticed and I was too young to drive. I still don't hear from my mother on my birthdays although she chewed me out big time when I forgot to call her on her birthday. Her excuse for everything was "Your sister like that girly stuff and you don't" and "I didn't want kids anyway"...both true.
I could whine on and on, I do that pretty well.
I've also learned that my cousins from my dad's side wanted very much to keep in touch, but were afraid to approach me because my dad and I had a very bad fallout years ago and, well, he is dead to me. For those cousins, I have to do the approaching and the maintaining, and hope that someday they will feel comfortable enough to call me for no reason.
That's my sob story (I can hear a tiny violin playing). I say be the one to call them if you are not too weirded out by it, but if you are feeling awkward about calling people that are family, then maybe it's time to replace them with friends, or pets. I live by the following saying:
"Family isn’t always blood. It’s the people in your life who want you in theirs; the ones who accept you for who you are. The ones who would do anything to see you smile, and who love you no matter what."
Can you accept them for being them?