Faint negative pregnancy result?

I have been on birth control for about two years and recently went off of it. My husband and I have been having unprotected sex then. I am currently 10 days late for my period. Right when my period was due I had light brown discharge for about 2 days. I took a Rexxal brand pregnancy test two days ago and it was negative. It's a test where you get a + or -. I got a - but it was very light and not dark like all other tests I have taken in the past have been. This is the first time I've taken a Rexxal brand though. Id there a reason that the negative result was very light? Should I retake? I have been under a lot of stress with graduating, final exams, and student teaching so I don't know if that's the cause of the missed period or if I'm pregnant.