Corporate America is the pits sometimes! I worked for a large company almost 3 years ago and had to deal with an awful boss who gossiped about me all around the office. She lied, even tried to get me in trouble with HR telling them that I took 2 hour lunches a day and was at least an hour late to work each day and that I left an hour early each day. Truth is, she had no idea when I left work since she left daily at 2pm to go to her "chiropractor" from an accident she'd been in literally 20 years prior. When I got pregnant and told her, I heard all the same stuff. I ended up quitting shortly after I announced my pregnancy because things got so bad. This woman was breaking every kind of HR/privacy rule known to man but she was super tight with the HR Assistant and Director so there was nothing I could do.
Doesn't sound like there is much you can do either. There are some women that are petty and immature and gossip just for the sake of something to talk about. If you took the matter to HR where would it really get you? Probably just make you an enemy and that isn't what you need. My only advice is to keep quiet on anything personal. Unfortunately you got bullied into telling your secret too soon. I'm not a good liar either so I would have done the same thing. I got screwed over so many times when I worked because I felt I could trust people. People that I thought were my friends. When those girls come by to gossip, just smile and nod. Sounds stupid but I tell ya, it's a jungle out there! Women are ruthless!
I'm very sorry to hear that you are having these problems, it isn't what you need being pregnant. Good luck to you, hope it all works out. :)