Period predictor/Am I pregnant!

Kelly
Glow originally predicted I would start on Saturday... It never came so I selected late and it changed uts perdiction to today, Weds. TTC for 2 months, off birth control for 3. Ive had PMS symptoms but weird on and off dull cramps for a week. 2 BFN so far. Whats up? Also why does the prediction change?