I had the same thing totally. Am 32 weeks now so just looking forward to my happy event - but at around 20 weeks I thought I couldn't go on. It was around Xmas and while everyone was enjoying boozy lunches I had deadlines up to the eyeballs. The attitude was 'she can't go out anyway so she can do it'. A*seholes.
Just remember that YOU and your baby are the most important thing. Office politics is what it is - if it wasn't you and your pregnancy it would be something else. In a few months' time you won't even be thinking about these stupid people anymore.
If you are worried about dirty tricks, do keep a record. But most importantly, make time to do stuff for yourself like book a massage in your lunch hour (I did acupucture and it helped me loads. I know it's expensive - my husband is out of work so we're not loaded - but for bringing me back to 'myself' it was really worth it). If that's not your thing then even 20 minutes outside if it's not raining will lift your mood. If you are physically up to strolling or other light excercise it is great 'me' time and will boost your emotional as well as physical strength. Make sure you are not taking the stress out on yourself by eating non-nutritious food, skipping meals or staying up late etc as that'll just heap more pressure on your body.
If you are not getting a lunch hour or aren't able to leave on time then they are properly out of order. Do whatever it takes, book lunchtime/after work as a recurring 'meeting' to show you're unavailable, or just tell people you 'have an appointment'. Take time in your day to call/text/email people who make you feel good - your partner, friends and family. It will remind you how much you are loved and valued and maybe lift your spirits with a few smiles or a good story along the way.
The most important thing is your own peace of mind and ability to keep toxic people at arms' length. Be kind to yourself as you really deserve it at this time. Mother yourself!
Keep posting and let us know how it goes.
x