Severely depressed.

I'm 16weeks pregnant. I'm very very depressed. To the point where I don't feel like I can handle like anymore. Not exactly thoughts that I want to kill myself just that I feel like I would be better off gone. I have always struggled with depression and the last 2 years PTSD. I don't want to talk to my mother who I always talk to because my brother overdosed on heroin twice in a year and so if I tell her sometimes I feel like it'd be better if I weren't here it really hurts her even though I don't intend on dying. I have a therapist but I can't work on my trauma because I'm pregnant. I just can't take any more, I feel like a terrible mom.