I really need your advice guys!!!

Me and my boyfriend are thinking that I might be pregnant, test came out negative but it was a cheapo and I am showing all the symptoms. I have had one child before, who my nmom now has. I gave her to her when she was about 6 months because I was not stable in any form and when I tried to get her back a year ago my nmom and nstepdad guilt tripped me into letting them keep her and adopting her (she is 6 now). I have considered going NC with them for awhile now but I am scared about what they will try to do if I do not let them have contact with this child when it is born but I am also afraid of what they will do if they do have contact. I have found out through family that they frequently talk bad about me and make out the abuse I endured my fault and not theirs. I know they are going to tell my daughter this and try to make me look like the bad person, they've already tried it on my facebook but my friends have seen through it. Any advice you guys have on what to do would be appreciated. There is much more to the story on why I want to go NC but I don't want to write a wall of text. I am bipolar and I am already afraid that people are going to try to use my disorder against me so this makes me even more fearful because they are N's.