why does my mom treating me this way?

ok let me start by saying im 21 years old, my mom and i have always had problems but since i had my son things have gotten much worse between us and she blames me and my older brother for her being sick(she has a budging disk, lesions on her brain and spine)

but anyways i love my mom so much and i always wanted to have a great mother daughter relationship, i was never able to talk to her and i have a bi polor disorder basically i cry more then normal people its how i let things out, i always tried telling her this but she has continued to say the same thing through the years like "stop being a baby, grow up" and "stop crying like a baby" anyways i still live with her my fiance(4 1/2 years together) moved out and moved back to our hometown where our friends and family live(my step dad is in the military, but he transferred back to our home state so we are only 2 1/2 hours away from our friends and family)so we could get our lives started as a family, i tried talking to my mom and step dad about it in a restaurant to where they wouldn't cause a scene, but it didn't work all i said was me and my son(7 months old)would be moving out very soon and she got really angry with me saying all these hurtful things like "your a huge disappointment" and "i have no daughter" and "your gonna fall" and that when i move down im gonna go party all the time and leave my son with anybody, when she knows i never go out even before my son was born i quite my job to stay home with him, i don't really trust day cares, and today things got much worse she took me off her facebook account as her daughter, came in my room started yelling at me again threw all my stuff down on my dresser and entertainment center took my tv and threw my computer down dented some stuff but didn't brake it(i tried talking to her yesterday and i told her i felt like a prisoner, because i cant drive, i cant go anywhere unless she says its ok or else she will get mad, and her name is on my account so she has total access to everything i have) scared my son poor baby started crying called me angrateful *****, said shes going to make my life a living hell, and shes going to call child services on me, im getting to the point where im scared of her, its like through the years she has gotten much worse, i feel like a bad daughter but i cant let my son live in this hostel enviorment anymore, i need to move out but im scared of what she might do, i just want all the fighting to stop, i have told her that im scared there is something mentally wrong with her because mental illnesses run in my family i asked her to please get checked out not to be mean (my brother gets SSI and my grandmother is in woman's home)im trying to raise my son on what i think is right and she gets angry when don't take her "advice" in my opinion advice is there but doesnt mean i have to take it if don't think its right for my son, like i said i love my mom but i cant take it anymore, i have tried for years every time we fight my hands shake im so scared im going to go into a nervous break down if i stay here, i told her im trying to be an adult and make my own decisions, i try tell my fiance so i can have somebody to talk to but she told me to stop telling him what goes on it in this house, really who am i suppose to confide in if not my fiance, she said i hurt her by wanting move out, i told her thats not not what im trying to do, she said that if she ends up being in the hospital on her death bed she gonna make sure no body calls me(that freaking hurt)

am i a bad daughter?