I honestly don't even know what to type to you, and I probably shouldn't be. I'm also pregnant, 32 weeks as of today. I suppose I could throw a bunch of "how could you"s and "shame on you"s your way, but you knew how bad this was before you did it, and still chose to.. ultimately you're the one with the responsibility. I do hope that your baby is ok. And you're right, for every drink you take, your baby takes THE SAME drink. At 17 weeks a fetus is around 5 inches from head to butt. I don't know if you feel him/her kicking quite yet, but as I type this, I have a mini kickboxer in my belly reminding me how much more important just about everything else in the world is, besides MYself and MY wants.
My only advice to you would be to really really think about your priorities. Come clean to your obstetrician so they can at least do some extra checking to make sure your baby is ok.. not doing that would be incredibly irresponsible in my opinion. As for mom and grandma, don't blame them for being horrified.. but I'm sure they're also sad, and scared for your well being, and that of your children. If you would drink now.. when wouldn't you? That would put the fear of you know what into anyone who's involved in your life.
See and I said I wasn't going to type much. PLEASE get help. PLEASE get your baby's wellbeing checked by your OB.. maybe coming clean will force some added accountability on you. Approach this as the wake up call from whatever higher power you believe in that it is, and hold on to the change in your life that you can make now, that will benefit both of your children for the rest of their lives.
I commend your honesty, but now it's your job to do the right thing moving forward from here.