Just a phase. It won't last and soon he will come up with something new to confound you.
Hi there. Well, with three year olds, there is a huge wide range of normal. The best thing to do if you are concerned is to talk to his pediatrician and get a referrel to an occupational therapist or developmental pediatrition,
My son was diagnosed at 4 with something called sensory integration disorder. We started looking into it at just a little before three for some of the same things you mention about your son.
Sensory integration involves the nervous system and processing. Motor planning is a componant of the sensory system and this can affect many things including speech. There are three parts of speech, receptive (taking in what someone says to you), expressive (organizing thought and thinking of how to respond and expressing yourself) and articulation (making the sounds of the words). You have to have all three in place in order to have proper speech. Perhaps your son has a break down in understanding what is said to him? You can test this by giving him some simple 2 or 3 step instructions and see if he can follow them. (point to the door, turn a circle, walk to the door, that kind fo thing). He may have trouble with expression as well. And how does he sound when he does speak and artiuclate the words? Is it clear (ish . . . he IS only three). Motor planning also affects things like fine motor skills sometimes---- holding a pencil or crayon. How does he do with that? It can affect gross motor? Any trouble there?
Bumping into people is something my son did/does. He doesn't get the proper processing of where he is in space--- bumping is a direct signal. It gets input into the system in a quick way. (al be it, annoying to those he bumps.)
My son finger rolls, flaps a little and spins. It is gaining input into the nervous system as well as a self calming technique.
I want you to know that my son is now 8 and doing FANTASTIC. Occupational therapy really addresses his nervous system issues and gives him coping skills and he is doing great. Many don't know he has this delay, he has friends, he functions pretty darn well. So have no fear, they do amazing things with our kids these days.
So, google sensory integration disorder also called sensory processing disorder and see what you think. Another thing to look into is the autism spectrum.
Lastly, if you live in the US, the public school system takes care of public early intervention. They by law must evaluate kids and if/when they identify a problem, these children are enrolled into the early intervention preschool and provided help and services. Something to think about.
Hang in there. It IS hard but from a lady that has walked this path . . . and come out the other side, hold onto hope and faith. They do amazing things for our kids now!