Dear Trisha,
Your son is at an age when one of the challenges is to learn effective ways to manage the flood of frustration and anger that often accompanies denial of wants/wishes. The fact that his problematic behavior is occurring at home and not outside the home is one sign that it is probably an example of a normal spectrum child behavior problem (vs. a sign of emotional disturbance).
Immediately on the occasion of any aggressive behavior, such as hitting or throwing things, you should place your child in time out (an adult-size chair or the bottom step of a staircase) and, using a portable oven timer to track the time, have him remain in the chair for five minutes (but start the time only when he is seated and quiet). You can talk with him about his behavior until you are blue in the face, as they say, and he will not stop it. He will stop it when he experiences that it is in his vested interest to stop it.
Take a look at SOS: Help for Parents, by Lynn Clark - it is a wonderful: manual re: handling of everyday behavioral concerns.
My 6 yr old started doing the same things when he was 4. It was a month or two after his MMR booster. For him this booster seemed to change him into a person we didn't know and had never seen before as we had no problems out of him before that.
After many hours of research on the Internet, we eliminated artificial dyes, flavors, and preservatives from his diet. We also added essential fatty acids; we use Efalex (efamol.com). You must have the correct balance between the Omega-3 and Omega-6 fatty acids. Supplement with extra DHA as one study showed that 480 mg per day of DHA - along with the other EFAs - gives great improvement in behavior. My son also apologized after his outbursts and said he did not know why he could not control himself. And he could not. He does much better now - is polite, obeys, is compliant, and only has normal 6 yr old defiance instead of out of control tanturms.
Try reading "The ADD Nutrition Solution" by Marcia Zimmerman, "Special Diets for Special Kids" by Lisa Lewis, and "The LCP Solution" by Stordy/Nicholl. All of these can be purchased at Amazon.com.
To help with your parenting skills and to better understand his behavior, try reading "Power Parenting for Children with ADD/ADHD" by Grad Flick, PhD and "Taking Charge of ADHD" by Russell Barkley. "The Defiant Child" is an excellent book for parents also.