I respect Cflas's post, but have a different view about this. I feel that if you were so intoxicated that you can't remember everything, then your capcity to think clearly enough to say no was deffinately affected- at the very least, your judgement was certainly affected.
Sweetie- whether this guy was 18, older than 18 or younger, if you were not coherent enough to make a sound choice, then what he did was possibly, at the minimum sexual abuse. He took advantage of a young girl who had obviously been drinking.
If you feel it was rape, then you need to tell someone. I know you aren't legal drinking age which isn't a good thing to begin with, but that doesn't take away from the fact that you feel like you might have been raped.
It's best not to ever place yourself in a situation like this. There are guys out there who wait for an opportunity like this, knowing that when an underage girl drinks, she normally goes way above board and gets to the point where her guard is down, her judgement is impaired and they are easy targets. Please, please, in the future, take care of you. Don't allow this to happen sweetie because you are young and have an entire life to live. You will be an adult soon enough, but for now, please try to enjoy the blessings of youth.
Be Safe! Take Care, and know that we are all here for you.