Brown blood is definitely old blood and less of a problem than bright red blood. You are probably losing the last of whatever you have to lose (sorry, I realise this must be sensitive for you). It happened to me when I lost a twin with my last pg. To be frank with you, I lost more brown blood (about a week or so later) than I did red blood at the time of the loss and it was pretty scary. If you are at all worried, get in touch with your GP.
I am so sorry to hear you MC, Its a horrible time. How are you feeling emotionally?
When i mc i has a d&c, i bleed for about 10 days after, The brown blood is old blood and like bunny2 said i would be more concerned if it was bright red. The clots are ok, it is excess tissue. Even when i had a d&c i had clots after. But my doctor told me this is fine.
My periods were longer after d&c aswell.
Hope this helps.