Im experiencing this too with number 4 on the way. With my other ones hair grow like crazy but now it is thinning. My dr said it cuz of pregnancy hormones n he gave me some vitamins to help. So talk to ur dr about it.
I am in a separate boat...my hair grows a ton and gets extremely thick while pregnant but doesn't fall out after...just keeps getting thicker...I just got it thinned and cut;)