Forgot My Dad's Birthday Again

I feel like such an awful daughter. I've been so wrapped up in my thesis and grad school stress that I completely forgot it was Dad’s birthday last week. He loves his birthdays, and this year he even hinted around a few times about how excited he was for another milestone year. And here I am, still trying to figure out what gift to get him because I couldn’t think of anything on the day itself. My mom is going to be so disappointed in me. How do you make it up when you just can't seem to remember these things? Am I really that self-absorbed?