I am afraid of my cat

my cat for 3 years now, she was a stray about 6 months old when I brought her home. After about a year she started biting and scratching me. She would let me pet her and purr and seems like the sweetest little thing, than she turns on me. When I sit down to watch tv she will come up and start biting at me. Bedtime is the worse she jumps up on the bed and wants me to pet her then she bits. If I cover my head she paws and bites. I look her out of the room and she will cry and scratch at the door. Twice she has hissed and swatted at me out of nowhere. My boyfriend doesn't have a problem with her, they play and when she is in attack mode with me all I have to do is stand my him and she leaves me alone. Once she wouldn't let him out of the room because she was hissing at him, I distracted her and put her outside until we were ready to leave for work. I let her back in and when we came home she was fine. What is wrong with her? Can this problem be fixed? I don't want to put her outside. I am afraid that if I would have a child someday how she will be with it. I am afraid of my cat.

At the risk of stating the obvious, get rid of the cat.
   
He is your pet but you are scared of him. Clearly you are not enjoying him if you live your life in fear of him.
   
Life is too short to spend it tied to an animal you are feeding, scooping litter and footing the bills for but don't actually like.

Thank your for your post. I know that the obvious would be to get rid of my cat. Its sad for me to even think about getting rid of her though. I love her and she is part of my family now. I was hoping to find some advice from someone with the same situation. Will she grow out of it? I am afraid someday she will turn for the worst, is there something I cant do for her. Your right I do feed her and take care of her litter and give her treats. I provide her with a good enviroment, she is not abused, she is very loved. Understanding that she was wild when I brought her home at 6 months. I just want to know if I can do anything to help the way she is.