The book is excellent, I think every parent should read it! I also firmly believe that you did NOT cause this. NOT NOT NOT NOT NOT!!!!
I think the docs are idiots for wanting to wait to do anything, because the earlier interventions start for most things, the better things are. I think you need to get into a Children's Hospital ASAP. I would look for a primary care doctor who would refer you to a neuropsychologist and an Occupational Therapist and a psychiatrist at a major Children's Hospital. Given everything with his birth, you also might ask for an autism specialist and a genetic counselor too. They will want to know why. I would give the history of his behavior.
To start everything, and because it takes time to get in to all the doctors and you want to have info to help them all, you should start writing a Parent Report. You have a VERY complex little boy here. It is going to take a LONG time to figure out what is going on. A Parent Report is a report that you write about your little boy that tells everything you know about him. You can follow the link in the bottom of my signature at the end of this post to find the outline for the PR. Moms who were on this forum years before me came up with the outline and it is amazing. I can honestly say it was one of the most powerful tools that I had when helping my Difficult Child get the help that he needed. He came from the point where we couldn't live with him safely and we thought he was going to murder someone to where he is now a productive member of society and a very loving member of our family. It really helps keep everything organized and at your fingertips and easy to communicate.
Know that unless a child is truly psychotic, they do NOT rage for no reason. Their reasons are not always those that make sense to an adult, but they have reasons. If you can get past your anger and see their reasons, you truly can learn to avoid or head off many of their outbursts.
Also know that for many little kids, and especially little boys, lack of regular protein and having too much sugar or simple carbohydrates will often make it hard for them to control themselves. I was often called the 'weird' mom because I always had a car and purse full of snacks and they were not the cookies and fun junk. I had stuff that had protein bars or peanut butter and crackers or whatever I could bring that was more protein than not. I baked cakes from scratch for school parties and snuck protein powder into them (kids never knew and begged for seconds, lol) so that the kids were not just sugared up and too hyper. I freely admit that this was partly because both of my sons got mean when they had too much sugar. If you add more protein to your son's diet, it may help, especially between meals. My youngest went through a period of time where he had tantrums after school. I learned that if I kept protein bars (at least as many grams of protein as carbs in whatever the snack was) in my purse and gave him one just as soon as I picked him up from school, he didn't have that meltdown. That year his class had early lunch and it was 4 1/2 hours from the end of lunch until school was out. It was just about as long as his poor little body could go without fuel without a major malfunction.
I don't know why this seems to be true more often for boys than girls, but as I have spoken to parents over the years, girls moms don't seem to notice an issue as often as boy's moms do. I could be completely wrong, but that is what I have observed.
I hope this helps a little.