What Causes Delayed Periods, Hip And Stomach Pain?

hi, im currently taking cerazette i have missed one and taken a few late, my period is due tuesday yeasterday and today ive had a smallbit of brown spotting my hips are painful at times and had shooting pains in my stomach, is this the beginning of my period or could i be pregnant ? for the past week i have struggled to get up in the mornings but do work shifts.