How do you disguise that your ttc/avoid drinking etc

Katie • 27 years old, married
Hi all 
​I'm after some good ideas on how to get out of drinking at a party without making it obvious we're trying for a baby. My friends all did the 'I'm on antibiotics and can't drink' excuse and I feel il be seen a mile off if I try that. 
​Any other good suggestions?! They already have their beady eyes on me as we've married nearly 4 months. 
The party is this Friday and I won't find out for definate until Saturday if AF shows so want to be cautious. 
​What are your best tips for hiding your plans/news?