What is going on with my 3 year old?

My 3 year old daughter is very bright and loving. Since the age of 2 she has changed so much, my main concerns are as followed...... When she gets very angry she screams in rage and hurts herself either by biting or pinching. She seems to have a hard time concentrating on anything ( I am not sure if this is the age or another issue) For example when we color she will color all of 2 minutes and then get up and start messing with everything she is not supposed to play with. Today I was working on teaching her the letter A. She lost interest right away and even though she would seem to know the letter not even 30 seconds later when I asked her to show me what the letter A was ( it was the only letter on the board) she would call it other letters. Any activity that we try to do she is like this. She hits other children for no reason during play and this is something that is new, her vocabulary is outstanding and we discuss how she is feeling all of the time but she still tries to hit in a sneaky way. She is abusive to animals when she thinks no one is looking as well. Her father and I are divorced and she has been back and forth quite a bit since 15 months old so I think some of this is acting out due to lack of structure and constant changing environments but at her fathers house last week she got angry and cut someone with a box cutter, I could not believe it ! When I asked why she said she was just angry. I am worried about her hurting someone or herself and I am concerned she will not be able to learn in school because she cannot focus. Any ideas what is going on here and what I can do to help her through all of this?

[Gina04]

Sounds like she may have ADHD and ODD.  My son has been diagnosed with these.  I would have her evaluated by a developmental specialist.