I read up on this about a month ago, me and my b/f had a scare and I wasn't sure if my period was a miscarriage or not.
You can have cramps with miscarriage, but there will be alot more blood, and liver like clumps (if you will)... the bleeding will last longer and be heavier... Believe me you'll know... I was told if you think you've had a miscarriage keep the "stuff" that comes out and take it to a Dr. to have tests done so you can figure out if it really was a misscarriage...
Hope this helps somewhat!! There are alot of great websites you can find info too!! Good luck!!