This happened to me too. The hormones you make while your pregnant prevent the hair that would normally fall out from doing so. Think back to your brush during your 9 month pregnancy.. how often did you actually have to clean your hair out of your brush (me? I never did). So all that hair that you would have had to clean out of your brush is now falling out.
Mine was soo bad that my sister complained that 2 weeks after a visit she was still cleaning my hair up! Whats worse is that my son managed to eat a strand of my hair, and I had to pull it out of his hiney after a poopie lol.
You will end up with the same hair thickness you started with. It took my hair about 3 or 4 months to finish falling out. It can be scary but it is perfectly normal.
If your hair is falling out in clumps and leaving bald spots, which is absolutely not normal, you should talk to your doctor. But a 50 cent peice sized wad at your shower drain is perfectly normal.
Good luck with your new baby!
J.