I am 7wks4days pregnant with twins, and have brown spotting since dec 18th or so. My nurse told me they think it can sometimes be from your body producing high levels of progesterone. ( I am also on progesterone shots). In my case, she said she would bet it stops around week 8, when I stop the shots. I am down to every other day for my shots, and it is tapering of. So, hang in there, call your nurse, and keep the faith!! Lots of women have brown spotting, and go on to happy healthy pregnancies :).
From what I have learned you can have light brown discharge and have a completely healthy baby. Maybe call the nurses hotline just to be sure.