5 days ago my pants where stained wit a very dark brown discharge. Since then I have not had anything more just a very bit of spotting when I wie. Barely noticeable. I am due on 3rd Sept. I have a 28day cycle. No cramps. Nothing.
What could it be?
In may this year I suffered a miscarriage and had a d&c.

There are a number of possibilities:

It may have been from ovulation. Some women may notice a bit of spotting at that time on occasion. It could be just from a change in hormone levels due to your period about to start. Or it could be due to implantation if pregnancy is a possibility. Some women will have a bit of mid cycle discharge or spotting due to hormonal birth control.