Reasons for late period? (def not pregnant)

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I'm 36. Had a baby in November. I'm not breastfeeding (chronically low milk supply).
Period returned in January, regular since. It was due 4-5 days ago.
 
I have had a jawline breakout for days now (unusual).
 
Not even a hint of a period!
 
Pregnancy test this morning was a definite negative. We're not ttc. I'm not taking birth control.
 
What's going on? Thoughts please!