I've had problems with hair loss too and am currently being treated by an endocrinologist for hormonal imbalance and nutritional deficiencies. I haven't regrown all that I've lost, but I've regrown enough that I feel confident and was able to ditch my wigs

(yes, it was that bad).
Your first step would be to determine what is causing the hair loss. Iron deficiency is the leading cause of hairloss in women, so I would definitely get your iron levels checked, especially the feritin level--this is a measurement of a protein in the blood that stores iron. Many women may have "normal" blood iron levels, but their feritin levels are depleted, so the body robs what would normally be used for hair growth and uses it for more essential bodily functions.
Another nutrient deficiency that is common with hair loss is Vitamin D deficiency, especially for those (like me) who live in northern states. Vitamin D is essential for many body functions, including hair growth AND metabolic function.
Sadly, weightloss can contribute to hairloss, so making sure that your diet is being properly supplemented is very important (and not all vitamins are the same--some brands are more effective than others).
Other common causes are hormonal imbalances (hypothyroidism, polycystic ovarian syndrome, use of hormonal contraceptives, etc).
The biggest thing is that the vast majority of hairloss is caused by internal reasons, not external (misuse by overstyling may cause breakage, but if your hair is shedding excessively and not growing back, then it's an internal problem), so I would definitely advise seeking a doctor's assistance in determining the cause of your hairloss.
Sorry for the long reply--it's obviously something that's been a sensitive issue for me and something I feel strongly about spreading the word on!!
Good luck and keep us posted.