There will always be some "reason" to drink. I drank because I was alcoholic. Birthdays, Tuesdays, angry, happy, tired, bored, excited, whatever.
A birthday is a day to enjoy, not wake up the next day hungover and feeling guilty.
Plan something exciting that you've always wanted to do. Skydiving, white water rafting, waterskiing, rock climbing. Something that doesn't lend itself to cocktails.