S.W.
I am 53 and have still not experienced perimenopause or the real thing. My periods are still like clockwork (or an old clock at least) and none of the common symptoms are happening. That doesn't mean that you aren't/haven't at 42. The age range of these changes is quite broad and is affected strongly by genetics. If you know the age your mother went through it, you will have a better idea of your own path. My mother was still having regular periods at age 56 and less frequent periods at age 58 (the age she was when she was killed by a drunk driver).
http://www.webmd.com/menopause/features/menopause-age-pre...
Peri-menopause means "around menopause" and is the name for the months or years that women have any or some of a list of possible symptoms because the amount of estrogen their body is producing is lowering. Menopause is the state of having been without a period for 12 months in a row. So, perimenopause is the journey and menopause is the destination.
http://www.webmd.com/menopause/guide/guide-perimenopause
I'm curious why your GYN put you on medication and for what reason, and why she hasn't talked with you about the blood tests. This article describes the tests that can be done.
http://www.mayoclinic.org/diseases-conditions/menopause/b...
I would want to know for sure if this was menopause or something else that needs to be addressed.