Why is my normal 28-day cycle suddenly 30/31 days for past 5 months?

I am 31 years old. I have had completely regular, almost down to the hour, periods at 28 day cycles for my entire adult life. Five months ago I had a period that was late by exactly one week. I keep track in my planner so that I know when to start wearing pads. My husband and I are using protection so I was surprised that my period was late, but I took a pregnancy test EVERY DAY until I got my period. I wasn't pregnant, so my period wasn't disrupted by a miscarriage or anything like that.
Since that month, my periods are now every 30 or 31 days. What is going on? My OB/GYN just said that's "normal" and maybe it's MENOPAUSE!!!! Again, I'm 31 years old with a completely, totally, reliably normal cycle. I see no reason why it would suddenly change like this... maybe gradually, but not suddenly. Any ideas? I have changed nothing about my routine, diet or home. Tweet