Your additional information leads in the direction od some developmental problem, but the only way to figure this out is through an evaluation. You will be making a mistake if you try to handle this by yourself. The book you are planning to read is very informative, but for practical plans re: management of behavior you will benefit more from SOS: Help for Parents.
I also wanted to add, my child can be affectionate at times but it is always on his terms. Sometimes if I rub his leg or ask for a cuddle he grunts at me. Is this a contol thing or soemthing else as with the above issues? He also is still in diapers at night and has no desire to try to go dry. I've tried everything and he just isn't bothered. He was premature by 5 weeks and weighed 3lbs 11 oz due to my SLE Lupus but had no apparent health problems apart from being small. I relaly need help as he can be a sweet little boy but his lack of empathy (though his teacher says he wants to please - although he does get in trouble for pushing etc - about 7 times at school sicne Sept). Is this mild autism, ad/hd, or just a behavioural problem? I am ordering the book The Challenging Child and hope this will help me but want to get to the bottom of it if there are problems that need addressing medically.
It is true that it can be difficult to diagnose ADHD at a very young age, but it is possible. Nonetheless, the sort of aggressive behavior he displays is not symptomatic of ADHD and, even if he does display ADHD, he clearly has other difficulties as well. At his age, it may well be that the most sensible plan for intervention will ultimately be a systematic plan of behavior management (for such a plan see Lynn Clark's book, SOS: Help for Parents). But you should definitely arrange an evaluation with a pediatric mental health professional to clarify the diagnosis and develop a plan for intervention.