What Causes Light Brown Spotting,nausea And Breast Tenderness?

I have been spotting for the past four weeks varying from light pink to light red with the occasional tiny clot two weeks ago I had two days of light brown im now feeling nauseous on and off all day tired tender boobs urinating more very light cramps in my lower tummy and light headed all this whilst on cerazette could I be pregnant or is it something else