Your son's behavior is entirely typical of a child his age. He can't tell you with words how upset he is, so he's using behavior to express his frustration. Ignore the head banging if you can. Guess at what's upsetting him and then put words to it for him. Show him how to solve the problem or redirect him to an interesting alternative.
Children with the autistic spectrum of disorders use repetitive behaviors as a form of self-stimulation, to calm themselves, to give them additional or alternate sensory input, or to fill in when bored or when overwhelmed with life. A specific upset often isn't obvious in observing those children. Other repetitive behaviors such as spinning or hand flapping, for example, are often present as well. Children with severe mental retardation also may do some of these repetitive behaviors.
However, that isn't what you are seeing. If your child is growing well, developing normally, has typical play patterns, and is engaged socially, it's unlikely he has autism. He sounds like a very typical toddler struggling to cope with life's frustrations which is one of his main jobs at 13 months.
