Starting to get depressed?

I’m 19 years old and 21 weeks pregnant. In the past I’ve had depression and anxiety, but I’ve kept it handled well on medication. But now that I can’t take that medication, I feel like I’m starting to get a little depressed. my family, mostly my sister, has been stressing me out to no end... I used to be able to tell her everything but now everything I tell her, she makes it public news. She told people I was pregnant on social media before I ever even did, she’s the one who got mad at me when I got pregnant and told my dad, and she posts on her Instagram when we fight. I told her I dont want her around my kid because she is selfish and openly enjoys hurting people. I don’t want her to teach my son that it’s okay to hurt women, because she tries to hurt women by stealing their boyfriend. also my fiancé is very lovely and understanding of me when I’m having anxiety, but I feel like he doesn’t truly understand how hard it is to be pregnant and to go through all these changes and not be able to do anything about the hormones and the emotions.. he gets so frustrated with me. I’m scared to speak to the people close to me because they will yell at me if I say something slightly wrong... so I keep it in. It’s getting so hard. Does anyone have any advice.. I try cutting my toxic sister out but she comes back expecting me to just trust her again and tell her everything about my dramatic life.

Edit- I can’t take my medication because my doctors told me to stop taking it because it could cause problems for the baby. I’m going to try to get a safe medication at my next appointment, but for now I can’t..