Trust your instincts. Your son is more than a handful, and his behavior is not normal.
Ordinary parenting techniques work for ordinary children, but you have been trying harder than ordinary parents to help your child. The feeling of guilt is understandable, but remind yourself that it is not you that have failed. You deserve a medal for your many efforts, including the frustrating and elusive quest for an accurate psychiatric diagnosis and treatment, and instead, the medical system has, so far, failed you and your son.
You're going to have to keep trying, going further and further afield, to find a psychiatrist who is willing to treat a 3-year old child. ADHD is often comorbid with bipolar, so you're wise to rule out stimulants until bipolar has been ruled out. Ideally, you'd find a doctor who doesn't categorically reject the possibility of bipolar disorder in a preschooler, but it might take many months or even a couple of years before an open-minded doctor would satisfied that a bipolar diagnosis is warranted. In the meantime, it's theoretically possible to treat ADHD without stimulants, or at least to treat some of the symptoms of your son without stimulants — for example, Abilify or some other med might be prescribed to help control the aggressiveness.
Finding a doctor is is tough. You're more likely to find doctor in a large, metropolitan center, and especially a doctor affiliated with a research hospital. You may be able get a lead at http://www.bpkids.org/connect/find, and also try your state & local NAMI (start at www.nami.org).
Daunna Minnich
Moderator, JBRF Education Forum