What Causes Light Discharge Between Periods And Abdominal Discomfort?

Hi, me & my partner are trying to get pregnant, it's now the 15th of January 2015, but since a couple of days before Christmas I have had tiny bits of pink faded blood when I wipe, none in my underwear, just when I wipe. I get the 'blood' every other day? I have had weird feelings in my stomach, I have done a test but it says I'm not pregnant? What is going on??