Missed Period

Hey guys.

I am 9 months PP. I have been on the Pill for about 8 months now and have never skipped a period since starting the pills. However early Nov I had only 2 days of light drown discharge/bleeding. And have yet to have another cycle. Is it normal to all of a sudden skip a period when they have been regular? I took a pregnancy test last week during the day and it was negative. According to this app I am over a week late now. Thoughts? Thanks!