Here's what Philip Kingsley, trichologist and respected authority on hair and scalp health, had to say:
Post partum hair fall occurs between the 2nd and 7th month after having a baby. Having lasted over a year, it is apparent that you have a probable metabolic problem causing your hair to fall. Although you have had blood tests, you may not have had the right ones or they may not have been assessed correctly. For example, a test often left out is ferritin which needs to be at least a minimum of 80 on the scale. Also, you may have a slight thyroid anomaly. However, although you are taking supplements, they may not be quite the correct ones and it is important to eat correctly as hair is protein. The most important meal of the day for hair is breakfast, and the second is lunch. Ensure that you eat adequate protein in these meals.
Also, I make a pure protein supplement called PK4Hair available on www.philipkingsley.com. Also, you can get a copy of my book The Hair Bible (2003) Aurum Press, which discusses this topic further.
Further you can start some home treatments by washing your hair everyday. Massage the scalp for 30-40 seconds before shampooing. Preferably apply a scalp mask, I make one (Philip Kingsley Scalp Mask), and knead your hair gently. You should try this, but you may need more expert advice. But these tips should help you anyway.