Need a new birth control brand?

I've heard that girls may spot before their period due to their birth control being ineffective anymore. If so, is it just bleeding that it causes? Can it cause bad cramps and lower back pain? Because it's happened to me twice now. (I don't think I'm pregnant). Or could it be endrometriosis or an ovarian cyst? I'm going to the doctor today but I'm just curious as to what other people have to say about it.