You might want to consult a dermatologist. They have expertise in problems with hair and scalp, and there are many possible reasons for hair loss which they may be able to help you rule in or out.
I did this and found it very helpful when I experienced an episode of thinning hair.
I learned from previous experience that it's not always helpful, or even safe, for me to self- medicate with supplements, especially before I knew what the problem actually was.
For hair loss I was tested for several things, including thyroid and vitamin deficiencies. Also the dermatologist looked for signs of scalp diseases and hormone imbalance. Everything was normal, except for moderately low iron levels. The doctor suggested temporary use of an iron supplement, with re-testing within a few months. She did not promise that this would do anything for my hair, but advised it could be beneficial for my general health. Because I had a history or childhood anemia, that made sense to me, and I did take the supplements as advised. Did it help my hair? I don't know.
In my case, the hair eventually grew back, and I never did get an exact explanation of why it was falling out. Sometimes there just isn't one:).
Of course it's human nature to seek an explanation, even when there isn't enough real data to prove anything. So I came up with my own totally unscientific (post hoc ergo propter hoc
http://skepdic.com/posthoc.html) reason.
It happened after I had gallbladder surgery, although that doesn't prove anything , as lots of people have surgery and don't lose hair. But I also had a nervous hair-pulling habit. I was completely unaware of this until other people pointed it out! At least I learned to be aware and stop doing it, which helped. But there could have been other factors, which I may never know about.
However it appears that alopecia areata, which can cause female pattern baldness or thinning hair , is statistically pretty common as women age. The reasons for it are not understood as yet. Not that that's much comfort when it's happening to us...
http://www.nlm.nih.gov/medlineplus/ency ... 001450.htm