Hi,
There are links between oestrogen dominance, progesterone issues and thinning hair (obviously just in women). Women's hormones shuffle about and start declining in their 30s, long before menopause. And if you have PCOS or are overweight (I have no idea if this is relevant to you!) then hair can start to thin from that age onwards.
In my case, my hair was going drier and crinkly, on the top of the head, but it resolved when I received treatment for out of wack hormones. The hair was never bad enough to send me to the docs, while the hormone shenanigans was, but I was tremendously relieved when the hair thickened up again.
I encourage you to go to the doc and ask for a referral, if they are unhelpful. The sooner these things are diagnosed/treated, the easier it is for hair to thicken up.
(There's a book I read about this about 15 yes ago, when it happened to me, called What your doctor may not tell you about menopause. I've just looked on Amazon, and it was reprinted and updated in 2005. Well worth a read, even if you are still a long way from menopause age)