My parents dont like me...and bring me down

I am a teenager...I live at home with my parents...and they seem as though they do't realize it maybe...or at least they would never admit it...but all they do is pick me apart. They only say negative things about me...I NEVER hear anything nice...its been this way my whole life..and its mostly little things...but its constant and it makes me want to kill myself. I have very little self esteem, and have a hard time feeling even a little happy already by myself...and with their added remarks i just feel worse and worse all the time. For instance...I walked out of my room today to leave...and my dad said "youre wearing that out in public?" with a disgusted look on his face...and all i was wearing was a light blue shirt, a brown skirt, and light blue tennis shoes that matched my shirt. then i said yes, im not wearing anything obsene?? and he said "i just dont get how you manage to wear such strange stuff that doesnt go together all the time" and rolled his eyes and turned around...so all day ive been asking people, does this not match, is this a weird outfit...and theyve been saying its absolutley fine, it looks fine etc. So then later I come home and im going to my room and my mom says, "geez i didnt realize how big your legs are, they are pretty big wow" and just looks at me with disgust like usual. I know those things are very small and what not...but its constant things like that, i just feel very insecure, and depressed because of it. I remember when i was five years old...we got our school pictures back, and i remember thinking "i didnt realize i was that ugly" and i asked my mom if she thought i was pretty and she said "i wouldnt say you are pretty, but you are kinda cute" and ever since i realized that my mom didnt think i was pretty...ive always felt worried that everyone else thinks that too...and even when people tell me i am...i dont believe them...no matter how hard i try....ugh i wrote so much....anyway...my question comes down to...why do my parents say this stuff to me, why do they constantly say negative things? Is it that they dont like me, for whatever reason...or my friend says they are jealous of me, and they arent happy with themselves, and tearing me down makes them feel better about themselves...do you think it is either of those, or something else? I just want to know their motivation...because all i can think is that they are so disapointed in having me as their daughter, and they are disgusted with how i look and everything else.