It sounds totally normal to me..... I think you're doing great! Here you are, at a big milestone (a lot of us felt weird around milestones), you just went to a party where all your friends drank, the holidays are upon us, and you're going home soon for Christmas. That's A LOT!!!!!
Just try to accept whatever emotions come up and don't worry about what you should or shouldn't be feeling. Something that always works when I feel a bit down is to count my blessings - it works great!:ghug3