How do I punish my hyperactive toddler?

My 2 year and 7 month old is severely hyperactive. He almost never sits still. He is unlike any other child I have seen in that he has never sat down and played with a toy or a set of toys longer than 2 or 3 minutes. No matter how much we have attempted to expand his vocabulary, he can only speak a very limited number of words. We have tried many, many, many times to get him to share and play well with others but it still has not worked. We have given him time-outs, given all of the usual verbal admonishments, given small rewards for good behavior, and even resorted to spankings in extreme cases. He eats organic and no sugar added foods. We have remained consistent throughout his life. He still does not play well with others, refuses to share, refuses to listen, and throws tantrums almost every time he does not get what he wants. We are beginning to worry that he has attention problems or some sort of severe behavioral problem. We are at our wits end, trying to find some way to get him to behave. Are there any suggestions of alternative punishments or methods of calming down toddlers? We are hesitant to visit his pediatrician because we want to avoid medicating him at all costs, realizing that ADD and ADHD are often over-diagnosed. Any help or insight would be appreciated.