this is my understanding.. so your trying to be assertive when your not, and people doint like it and they can see through it.
if you try to be overassertive people will.
so how about naturally building it up? i know it seems hard but when you reallise its working life'll be so much easier. start by just being prozac happy. think about all the good things youve got - friends, family, your appearance, your grades... then remember all the good times youve had. listen to feel good music. go out and shop..do anything to make you happy and hopefully naturally your confidence'll build and you wont need to pretend its already there.
its harder to stick up for yourself when your just finding it hard to carry on.
finally, make sure you can be assertive.. not agressive. cause then you really will pay for it.

am i right about what you mean?

x