You say that you and your mother don't have the kind of relationship in which you can talk about things, but the options are really, really limited if you don't at least try to talk to her about this. I would advise you to do it during a time when the two of you are alone and when you are not in the midst of an argument.

Try to stay calm, keeping the focus on your concern for the family and presenting your particular concerns about the impact of having to take care of your brother all the time.

Give her examples--something concrete. Maybe your grades are slipping because you're spending so much time cleaning the house and taking care of your brother's needs that you don't have enough time to do your homework, or as you pointed out before, that your social life is suffering because the house smells like pot all the time.

And don't forget your concern about her; her pot-smoking and going out a lot may be an indication that something else is at play. You say that your dad's no longer in the picture. If this is a recent break-up or divorce, then she may be experiencing depression and could be attempting to handle it in these ways. Ask her if she's okay and urge her to do something about her situation if she is down.

If your efforts yield no results, try talking to a school counselor who might be able to talk to you about coping skills or who may decide to speak with your mother about the impact the situation is having on you.

Take care.