I cant stand up for myself...?

I am shy and have ALWYAS been a real pushover..I got picked on at school, and even my friends didn't stick up for me in the most awful situations. My parents have even picked on me. Now Im 20 and I have some friends at university and some from near where i live. Some of them are my cousins and to put it frankly, they have all at one point or another treated me like dirt. Some of my "friends" have been so awful to me I wouldnt even want to go into detail. But the only reason they choose ME to pick on, I think, is because they know they can get away with it and they feel authoritive over me and it makes them feel good. Anyway in the ast couple of weeks I have tried sticking up for myself...just by telling them to get lost if they make fun of me or just saying that theyre wrong when they are horrible to my face or send me nasty text messages or say things about me behind my back...but they make me out to be the worst person in the world for sticking up for myself and its really hard work getting them to forgive me just for standing u for myself and i am the one that ends up apologising because i cant be bothered fighting with them any more and they have never once said sorry to me. I am at a dead end i just dont know what to do...If I stick up for myself, i lose friends and if i dont stick up for myself i get treated like sh*t and things get worse. please give me some advice...do i stand up for myself and lose all my "friends" and be all alone or do I hang in there and is it better to have horrible friends than no friends at all? please dont tell me to make new friends because 1. I am really really shy and 2. I reckon this is a problem I have, not anyone else...if it was any other person in the world I think I would get treated the same because i am a pushover... :( xxx