What Could Cause Vaginal Spotting?

i have a question.. i am on the micogynon 30 contrceptive pill and take it the same time every morningiv never missed a peiod.. well until this month. i had my last period on 17th nov 2011 and so my period this month was due on around the 15th dec 2011 but still has not came. i had a light spotting on 13th dec and thoght it was my period but it didnt last long enough it was just a light pinkish colour and lasted about 36 hours and now nothing.. my vaginal discharge has increased and is a golden colour i am also getting headaches nausea feeling and dizzy spells i took a pregnancy test this morning and it was negative could you help me please??