Hi Ayana,
I have heard from several friends that a children's calcium and magnesium suppliment was beneficial to their children when they were overactive, also to help them sleep. The omega 3 is a good suggestion as well. Hopefully you are able to take her to a doctor that is familiar with more natural remedies. Dr Sear's website has all kinds of good information. You might want to start at this link
http://www.askdrsears.com/html/4/t040400.asp#T040408 Also you might try keeping a journal or log for a few days noting everything she eats and activities she is involved in, the people that are around etc. This way it may become clear if there is anything in her diet or environment that makes creates positive or negative change.
As far as the head banging -- my son used to do this too. I use a technique called a "Locational" which basically gets his attention off whatever is upsetting him and puts his attention onto the environment. Now when he gets mad he sometimes will do a locational on himself. I will see him get ready to bang his head then instead he starts looking around at things in the environment. This gives him a technique so that he can handle the frustration and take control so that he can make himself feel better. It is also effective for those times when he has gotten overly tired to the point that it is hard for him to fall asleep. A link to how to do a 'Locational' is
http://www.scientologyhandbook.org/SH6_7.HTM Best wishes! Lisa