Can Contraceptives Cause Excess Bleeding?

I am female of age 28. I got married 5 months ago. I used Injection contraceptives two months ago. In first month I missed my menstruction but its been three weeks i am having continious bleeding...sometimes spotty type and often little bit more blood, but less comparing with regular mentsuction day. Please help me answering this question. is this side effect of contraceptives or something else?