I felt like this for years. For me, ultimately, it was a matter of a) not feeling like I deserved to receive any kind of special treatment or attention, and b) wanting to live up to others' expectations. Since I worked through those issues in therapy special occasions have been subdued into their proper place in my life!
This is not to say you share those issues.
I would say, though, that it IS SO OKAY for you to celebrate (or not) your birthday or Mother's Day exactly the way you want! Whyever would you celebrate by going out to dinner when you don't enjoy eating out?! Say no, Liz! It's okay!
And lastly, HAPPY BIRTHDAY!