Haven't had a period for 7 months & not had an injection for 8 months, started getting brown/red discharge and belly & back pain should i be worried?

Injection?: Depo-Provera injections for contraception can cause a long delay in the resumption of normal periods. Infertility for up to a year after the last injection has been documented. If this episode of bleeding does not turn into a real period, I might visit your GYN for an evaluation. If you are having pain, you could have something else going on like an infection or an ovarian cyst.