Does Brown Vaginal Discharge Indicate Pregnancy?

I am 28 and have a three year old and have been trying for another baby since she was born. It took us over three years to fall the first time (had endometriosis though thats gone now and both clear). I was due on last thursday and on the saturday had very weak brown blood which lasted 3 days then went. I had no pain at all. Usually my periods are quite heavy, reasonably regular with quite a bit of pain. This is really unusual as it seemed more like spotting and was browny with no pain. My period usually lasts three days so that was the same. Pregnancy tests negative. Could I still be pregnant or is something else wrong. Thanks