I lost a ton of hair with my first pregnancy. This time round my doctor recommended taking prescription prenatals instead of OTC ones, they are higher quality I guess. 21 weeks currently and no hair loss yet. Bonus, the prescription ones are totally free with insurance. :)
Are you taking your prenatal vitamins? Because I had the same thing when I was first pregnant because I didn't know I was pregnant and after I found out and started taking my vitamins my hair stopped falling out completely! If your not taking your prenatal your baby will take all of the nutrients it needs to grow and you won't be getting any
I also loss a lot of hair. I got my thyroid check because there is an historic in my family but it was fine. What help me is to wash my hair only every two days. Make sure your shampoo isn't too strong and there is shampoo to help with hair loss. Also I was told by my nutritioniste to make sure to eat enough protein because not enough can cause hair loss. I still worry because all my friends loss more after giving birth :s