I have a B.A. degree in psychology and whereas I don't practice in the field, I am familiar with disorders. I want to tell you not to panic when these other mothers/mothers to be tell you to get him checked out for Autism. It is a good idea to, because his behavior could indicate it, but on the other hand, it could also be just behavior that he has discovered gets him attention.
My suggestion would be to, when possible and when it won't endanger him, allow him to do what he is doing without reacting. I know that is much harder to do than to say, however, every time you respond to that sort of behavior, it reinforces him to do it. You tell him no, he bangs his head, you will allow him to do it just so he will stop banging his head. This sends him the signal that all he has to do is start hurting himself and you will cave in to his wish. So...make the environment as safe as possible, remove all the hard things that he would hit himself with and replace or cover them with something soft. You can even go so far as to staple bedding foam to the walls at his height for a period of time so that when he bangs his head against them, it won't hurt him, or make him a wear a helmet. That way you can safely allow him to do his behavior and give him no reaction. Once he figures that this isn't getting him what he wants, he will stop and find something else to do to get his way. If you do this, expect the head banging and hitting to increase for a small while. As long as it is safe for him, then you can ignore it.
As for the violence to you...when he does this, pick him up, and put him in his room, or make a baby-pin with the free-standing baby gates, or if he is still in a crib, put him there, and then walk away until his temper tantrum is done. Once he quiets down, you can then go back in and take care of him. If he starts throwing a tantrum again when he sees you, walk out of the room again until he calms down. He will eventually get the picture that this is unacceptable and that if he wants attention from Mommy, that he needs to behave himself.
Make sure the space you put him in is safe for him. I stress that more than anything with this method. If it is a situation where he can really cause himself injury, you, of course, can't pretend that he isn't doing anything. But if it is a place with a lot of padding, that you know he can't hurt himself in, then it is ok to walk away and let him scream and cry. It will be hard on YOU, because you will want to go and make it all better for him...but every time you do that, you reinforce to him that this kind of behavior is acceptable and that he can always get what he wants.
I am not a mother yet, but I helped raise my now 14 year old nephew for the first 6 years of his life, and he was NOT an easy child. He was also prone to violence as a toddler..to himself and to others. One thing I used to do with him when he started that was to pull him into my lap and hold him down until he calmed down. He was not allowed to get up until he was calm and behaving. I knew that in my lap, he was not going to get hurt and I could control how he tried to hurt me. I caution against this though, because your son may come to view your lap as a negative place and not want to cuddle with you. I didn't have that problem too much with my nephew, but it is a possible side effect. So, I suggest making a safe, cushiony, soft place for him to go to time-out when he starts acting up. Someplace that you can feel secure in leaving him in and walking away for awhile.
And do mention the behavior to your pediatrician and have him checked out. It is better to rule out biological reasons for behavior, then to ignore the possibility and have to come face to face with it later.