I am pregnant and being treated badly at work

To start off I’ve been with the company for 3 years. My manager and peers treat me very well except for the assistant manager. The assistant manager treats me poorly. She tends to pick at me no matter what I do. She criticizes me constantly. She’s extremely condescending and always puts me down in front of my coworkers. It’s gotten worse since I’ve gotten pregnant. Once in awhile she’s nice to me but that’s rare. The thing that annoys me the most is my other coworker is pregnant as well and she seems to give her a ton of grace when it comes to making mistakes. She always treats my coworker kindly and puts her above everyone else. I’ve talked to my actual manager about it and she is so nice she’s almost naive that anything is actually happening. She just tells me to ignore her which is hard when she is above you and can manage you. At this point I’m just going to take my maternity leave in November and never come back. Which is sad cause I actually like the company I work for…. This is kind of a rant I know but I’m so upset by it and it’s stressing me out.