If you really do not want on them you can just go off of them, but it seems very strange to me that you only went on them two weeks ago and you already want to get off of them. It takes three months for your body to get completely used to a new or first b/c pill so if you are having side effects they could very well go away. As for weight gain, if you go on the pill that is right for you then you will not gain weight.
Being on the pill is the best way to make periods normal, lighter and less painful. Even if you are not sexually active, I do not see why your mother would not understand that. Taking pain pills to calm the pain is one thing, but being on the pill would make it so there is no more pain. And your flow would be lighter and your period would not last as long. (in most cases) my period has always lasted the same amount of time, but it is soooooo much lighter and I hardly ever get cramps now.
Do what is best for you, but if your doctor recommended this, you really should try it.
But, when you quit taking the pill your body will be weird for a while because your hormones are greatly affected. You will probably spot, or may even get your period again right away. Side effects of going off of it could last quite some time.