I sure hope purpleknight does not drink now. I'd hate to have to break out a can of whoopass on him.
AA - alcoholics anonymous is the 12 step route. It is an organization of men and women who come together to talk about their problems with alcohol. It involves a process - usually with a sponsor (a proven veteran) to assit and guide you through the 12 steps.
See the 12 step forum for more details.
In my opinion you sound like you are ready for this. Stopping drinking that is. There are several avenues from which to choose. AA/12 steps is one option. There are others. It depends on your outlook and ability to be honest with yourself and being able to make a commitment to stop drinking. If you don't now, it will become more difficult later. You have great potential to become one of us who discovered too late how alcohol made a difference in our lives. Not a positive one.
I would tel MIL that you have seen a doctor - see a doctor - and tell her the doctor told you you couldn't drink for health reasons. Or just say you don't want to drink for health reasons. It would not be a lie.
Good luck.
Welcome to the forum.