L.S.
I would bet that you are low progesterone. Post pardum hair loss is very common because of the vitamin issues but also because you do not cycle normally for so long that your body is not producing progesterone.
I have 4 friends (and my own mother) that have started progesterone cream, bio-identical hormone not the progestins in birth control, and have regrown their hair with NO SIDE EFFECTS. As a cancer survivor, I can't urge you enough to avoid nioxin if you can. It is a toxin - not enough space on this forum to get into all that.
Even if you are having 'normal' cycles, you may be estrogen dominant from one of the follow causes: annovulatory cycles (normal cycle does not necessarily mean that you ovulate - only way to know is by checking basal temp), interference from toxins through milk/meat/veggies, hormones from milk/meat, taking certain prescription drugs, stress, being overweight holds extra estrogen around middle, taking hormones (the pill, IUD, HRT even low dose).
Very easy to use, relatively inexpensive.
Write me back if you want to discuss (obviously, I am obsessed with the research and think this is the best thing that anyone can do for their health!)
HTH
L.