Hi I Have Pcos N I Have No Periods For

Hi I have pcos n i have no periods for 2 months but now from a week I am having light brown spotting whenever I sit stand or moves on stairs.n yesterday I had mild backache n in evening had good quantity of brown bleeding n i again rest on bed it stops but whenever i stands up it happens again. My doctor told me to have cycloreg 3 times a day for 2 weeks and have pregnancy test on 6 march again bcoz my tests r coming negative.plz suggest?