Miscarriages in early pregnancy are very common. Sometimes there is no "cause". It could be that the egg did not implant well, your body is just not ready, possibly the alcohol, there was something wrong with the fertilized egg.
Many women will actually miscarry at this point in their pregnancy w/out ever even knowing they were pregnant. The fact that you knew at only 3 weeks is extremely early.
Many, many women will have a sip or two of alcohol before they know the are pregnant. Now, that is much different from going out on drinking binges every night. You oinly mentioned drinking on Thanksgiving. That would be a festive time to drink, but the way you said "and we drank" just made me think "we got drunk".
I'll admit that I'm a little prejudiced against you trying to get pregnant again right now. I think you are too young. I have a 17 year old son who is a Jr in high school. I shudder to think of him as a father right now. He is completely unready for it. He's killed 4 goldfish in 1 yr and can't remember to clean out the cat's litter box on a weekly basis.
You're the same age as my son, the same age as the little girls he runs cross-country with. It is hard for me to imagine any of them with a baby either.
As far as guilt - I do not believe you need to feel guilty. A miscarriage is not an abortion. You made no concious effort to get rid of your baby. You did not even decide to drink while pregnant, you drank unknowing.
But I do believe the miscarriage is probably telling you your body is not ready yet. You are still growing and maturing pysically. You don't have much more to go, but there is a little bit. If you are serioius about wanting a baby, take at least a year from the miscarriage to get your body in shape. I'm not talking about pumping iron at the gym (although some exercise is good) but improving your nutrition, cutting out most junk food - jut easting healthier, cutting out the alcohol and any smoking if you do so (which is a far bigger risk of miscarriage).
And talk to your ob/gyn. See what he/she has to say about your miscarriage and your overall health.