As has already been mentioned if you are pregnant, the baby isn't properly tapped into your blood supply yet so, in theory, drinking shouldn't affect it. That said, even if I was a big drinker (I'm not) and even if it was my birthday, if there was a chance I was pregnant no way would I be going out and getting smashed. Enough drinks to be merry, sure, but not falling about slurring/puking (and I'm not making ANY assumptions here! I'm not suggesting that's what you have planned! Just sayin', I wouldn't, yknow?)
As for the negative test at this point, again as already has been said, there is still a chance of it turning positive. With my first son I didn't get a positive until the day my period was due. With my second, not until the day after my period was due (what was with the most sensitive tests and they were absolutely negative a few days before). Some women, it's even later due to either slow rising hormone or the fact they ovulated later in their cycle than usual.
Oh, and whilst I 'just knew' I was pregnant with my first three kids, this little sucker took me by surprise - not a single symptom to make me think 'aha! I'm all up the duff again!'. So don't worry that you don't 'feel' pregnant either!
Finally, good luck with getting pregnant and have a great birthday! Just like all the adverts on tv for alcohol say these days: (given you might be pregnant) Enjoy Alcohol Responsibly 