You are medically not supposed to be drinking, right? Aren't you testing for liver enzymes? If someone offers you a drink, you can justifiably say no, without giving anything up, and also even have the right to get pissy with people if they keep pushing it on you.
Go to the store and buy yourself some "special" kind of drink, like those fancy fizzy lemonades from France or some Fresca and cranberry juice, so you have something "special" to drink at the party that is non-alcoholic. Or don't go. But don't give in to peer pressure.
Stay strong!