Hair falling out! Help!

so I've notice my hair has been falling out horribly... like when I'm in the shower it's a good clump that comes out...and even more when I brush it after and it will continue to have strands fall out during the day.. my hair is super super thick well I should say was! I swear I'm starting to get a bald spot on the top of my head... even my fiance has taken notice to the thinning. I said something to my dr. and she acted as if this wasnt normal and said that usually happens after birth in some cases. I started taking 2 prenatals a night ( oked by dr.) and I feel like its helped some but not enough to stop the thinning... I just want to know if anyone else has experienced this and if your hair came back to normal. I'm freaking out I'm only 23 and dont want to be balding already haha my stress is kinda high just from being a stay at home mom and dealing with Bill's and my fiance's business and the new baby but I dont feel that it's so bad my hair should be falling out... I've stressed way more (not pregnant) and it never happened. Please give me your advice or share your experience!