What Causes Delayed Periods, Weight Gain, Dark Stretchmarks Due To Depo-Provera Injections?

i have been on the depo injection for six months i stopped May, while on depo i gained a lot of wheight and i started having dark stretchmarks that look like blood cloths they are everywhere in my thighs and bums and now its July and my periods are still not coming. i took 4 pregnancy tests and they came out negative. i dont know what to do