I use Naturopathic Physicians and there are a few things they have suggested to me over the years with my 3 & 6 yr old girls:
Children sometimes act out when they are low on essential fatty acids. One of the fastest ways to correct that is to use olive oil directly on the kids skin like a baby oil, right under the ribs on the kids back. I have tried it with my kids and have had instant results from cranky kid to darling baby. Really good and easy to do. I now use it as a moisturizer for them and me - it rocks.
Lavendar essential oils can be very calming, either in a bath or on the kids feet, chest and forehead. I don't know if your child would have alergies to plants or something if this could be a concern - you might wan to check with a dr.
Not surprisingly, sugar is so very often the culprit. When they last said that to me I was so offended. I work hard on doing a proper diet for my kids - they said we just don't always think of how sugars sneak into our diet or how much is too much. I thought my kids never eat candy, but they drink a lot of juice and like PB&J. It's hot now, so the occasional popsicle or cookie, or tomato sauce, ketchup, fruit. It adds up.
Try to get your kid to drink juice only at meal times and try to slowly dillute it (of course making sure it is 100% fruit juice) and give them water at other times of day. The sports bottles are great for kids too (though you don't want flouride water either). Let them have only 1 sweet snack a day - less if you can get away with it, particularly if you do use a lot of ketchup or other products that have sugar as an ingredient.
Cow's milk is also said to be at issue these days - and when you understand that there is a cow's head on every bottle of elmer's glue because casein (found in all cow dairy products) is what makes the glue sticky. When that gets gummed up in our systems it can cause all sorts of problems. Fortunately there are goat's milk and rice milk products that are delicious and similar enough that young children don't mind the switch. Goat cheese is also a good alternative to regular cheese.
There are definitely things that can be done to help you both. Truly, no child's natural condition is to be contrary. A nutritional approach can be really helpful and easy to implement.
Peace!