My Hair has radically changed - HELP!

I am a 45 year old woman who for most of my life, until recently, had thick, naturally curly hair. Hairdressers marveled, men swooned, etc., etc. Now, in the last 2 years or so, my hair has thinned so much, it’s TOO thin. Also, in the front, it’s to the point it’s almost so thin you could call it on the edge of balding. My hair is more brittle, dryer, and the curl is all but gone. I don’t use hair dryers, didn’t need and don’t use permanents. I’m kind to my hair. But I really HATE my hair now. Nothing looks good. Cuts to make it look fuller fall flat. It’s lifeless. Help!

P.S.: I am not on birth control any longer, but once was. I have had my thyroid checked. No problems there the doctor claims. I don’t know who to believe…*sigh*

I was on the pill for hears, but stopped about 10 years ago, before this started. About 5 years ago, I began using vaginal cream with estrogen in it, but it is topical, not oral; my pharmicist assured me it should not have the same side effects. I have had testing for thyroid, etc. as I said, so unsure what to check next...