Excuses for not drinking?

So I just got a bfp yesterday and today through Tuesday we’re on vacation with my MIL and her twin sister! They have tons of fancy restaurants and wineries planned, and lord knows I never turn down a drink! They know this - so how do I navigate this long weekend?? I feel like they’d think it was suspicious if I told them I was taking a medication that caused me to not be able to drink because normally I would tell them ahead of time... but, that could still be an ok option. I also thought about just telling them, but it’s soooooo early! my period isn’t even due until Monday!

So, any tips or tricks??