Your mom is correct but what she is not telling you is that it is a HUGE exception for women to be pregnant and still have a period. It happens to extremely very few women. I think it is safe to say that you are not pregnant. You can take one more test to make sure.
Now for some preaching: It is extremely dangerous to get so drunk that you cannot take care of your self. In many cases this will be considered rape if you were not in a state to give your permission or stop him (and I am not saying that he raped you, I were not there and do not know the circumstances).
You have to consider whom you are hanging out with if they will do this to you. A condom is not just to protect you from pregnancy but also from STDs and STIs. It will be wise to have yourself tested for STDs/STIs after an incident like this at the very least.
Your own sexuality and body is yours to give to a man of your choosing. You should at least respect yourself enough to protect yourself from such situations. Get new friends if they knowingly allowed this to happen to you - they are not your friends.
You seem pretty nice so please take care of yourself.
Best of luck!!
