suntikan perancang /depo

Mcm mana nak hentikan period yg lama,almost 24 days.sy ambil suntikan depo,the problem is period sy x bhenti..how to stop it?1st time I took it,since I got cser last 2 mth..so doctor advised me to use it.sy risau...after 15 days period.. supposed to be I have to pray right?