I think you will find it is very common for people to have drunk before they knew they were pregnant. I remember telling my OB when I was preg with DD1 that I was so scared as I didnt' know for 6 weeks and had had my bday overseas....thus lots of drinking! Anyway, he said he hears that all the time and not to worry. Which was good advice because it was too late anyway! I just stopped after I foudn out.
Saying that I had two beers whilst pregnant with DD2 and then with DS1 I had a wine a few times (prob about 6 all up over the pregnancy.) I also had a friend that had a glass of wine each friday night while pregnant. Try not to worry on what's been done just focus on future. xo