I agree with the previous posters -- go get some advice from a professional. My daughter was the same way. I wanted to throw myself off a bridge daily from the time she was three until she was five or six (not really, but, man, it was TOUGH). I tried everything I could think of and was at a loss. All three of my kids are strong-willed and stubborn, but her behavior went beyond anything I could deal with alone.
Sometimes it isn't even a "syndrome" or a specific diagnosis anyone can make -- but information is power, and every little bit you know will help in strategies with how to deal with the disruptions.
Turns out my daughter is fine. She's ten now, gets straight A's and is in the gifted program, and behaves well about 95% of the time. She's just really sensitive and doesn't know how to show it and has anxiety (which Zoloft has helped immensely) -- and when you mix those things with a tendency to be inflexible and routine-oriented, it is a recipe for meltdowns. As she has matured, she has figured out coping skills and has been able to get more control over her bad feelings instead of acting them out.
And don't be afraid to try two or three places until you find someone who understands your child. There are a few counselors out there who have no clue or are just not a match for your family.
A great book to read is "The Explosive Child." Here is a link:
http://www.amazon.com/Explosive-Child-Understanding-Frust...
Good luck. I feel your pain!
L.