Dark discharge to lighter

So AF is due tomorrow so far my symptoms have eased up. Yesterday I had dark brown discharge a very little amount, alot of lower back ache too, the discharges eased up and eventually stopped yesterday noon. today its very little and light in colour. Is this normal I'm 4 weeks today. Took a cheap test and it read positive but lightly positive, though I've been having some bold FR tests.. Has this happened to anyone?. The back pain is there but not as intense as yesterday. Help please. Sorry for the try mi Pic

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