I'm unsure if I should even do anything for my girlfriend for her birthday and for Valentines day
Aren't those the days important for her and you as well?
I'm not sure if I should celebrate my girlfriend's birthday. What's her present to me?
You should give a gift to your girlfriend for her special days because you care about her, not because you expect something in return.  Her birthday is her day to celebrate, and Valentine's day should be special to both of you.  However, if she truly doesn't show any concern for you, in general, then maybe you would be happier with someone else.
I feel better knowing it's okay not to do anything for her for her birthday.
You can always greet her on her birthday and not give a present. It doesn't make you a bad person but be ready for the consequences that comes after.