Hi, I'll tell you about my own experiences which may or may not be the same thing as yours. In my early forties my periods starting getting irregular and I wrote it off to pre-menopause. After 6-8 years of irrgular/missing periods they checked my thyroid and said i was borderline, a few months later they said I was definitely hypo and started me on meds. The missing periods were apparently due to thyroid even though I wasn't clinically "over the edge" Now I'm horrified to find out that at the age of 49 I have osteoporosis and my back is curving from lack of estrogen because of the missing periods. I would have my thyroid checked again and start taking a lot of calcium while the doctors figure this out of I were you. I wish I had!