And then, thank goodness, the whole thing ends and you can really start to enjoy life!
BTW, to the OP, your dr is probably going to want to check your hormone levels, but believe me, that's a crap shoot.
My periods were like clockwork too. Then, one month I was late by a week or 2, and the period I had was weird.
More months, maybe 5 or 6 went by, and a period didn't come one month. I happened to be going to the doctor right at that time and mentioned it to her. She took all the usual bloodwork, and when the results came back she said everything was totally normal, and I shouldn't be experiencing often missed periods for a few more years. Internally, I said "yeah, right". I just knew.
The month before that was the last period I ever had. They just stopped. Bam.
I used to worry about being post menopausal, but let me tell you, it's AWESOME!