I'm sorry to hear about that.
In order to determine if you're doing something wrong, we'd need to know what you are doing. Could you possibly describe your husbandry in as much detail as possible?:
caging, lighting, temperature, humidity, food items, length of captivity, where you got the turtle, substrate, and a basic description of the turtle's behavior(daily activity, chasing bugs or not, eyes opened or closed, etc.)
I'm sorry for all of the questions, but this is a tough one. It could be anything from abrasions to internal organ damage. Dried blood at the corners of the mouth is a serious concern. If it were me, I'd take the turtle to the Vet. immediately.
Good luck. I'm sorry that it has taken a few days for someone to reply.