Help please ladies

Nina • married 2016 and we are trying to conceive.
We are currently trying to conceive and have been for 1 year now, I am due on my period and I do have all the symptoms but I am not bleeding I am just discharging large amounts of dark brown stuff, I am needing to use pads/tampons, I have previously been on the depo injection, ended 13 months ago but my periods have not been much but this is a first, what does this mean? X