Work advice

Rowena
Hi
I have a big work award party, which costs a fortune for the company for me to go. It's a free bar night and obviously I won't be drinking. I'll be 9.5 weeks by then. So far I've been nauseated and so tired so I don't think I'll be up to it, also I don't want to raise suspicions from my colleagues that I'm pregnant as I won't be drinking.
How do I get out of it? Should I tell my female boss the truth?