my period was 4 days late and had a light, spotting period then it stopped and now the spotting began again ?

I have been on Yazz birth control for 3 months. For the first two months I had a normal, regular, on time period. This last month I was 4 days late and it was a light in color and amount. I took a pregnancy test and it was negative. I had a spotting, light period for about 5 days then it discontinued. A few days later I had a light pink spotting. Then next day it went away and then the day after the spotting re-appeared. Now I am still spotting off and on. My period should be over. I have missed one pill this month but did take 2 the next day as directed. I took one in the morning first thing then one at my regular time. I have been under a lot of stress this month as well, could this be the cause? Is this normal? I have PCOS (poly cystic ovarian syndrome) as well so I am used to the irregular periods, however, the birth control was suppose to help w/ that. Do I need to be concerned?