From what you have described, your son may have sensory processing disorder. This is when a person's nervous system does not perceive input from the senses in a normal way. Some children are extremely sensitive, some extremely underresponsive to stimuli, and other seek out lots of stimuli, as if they can't get enough. There are varying degrees of spd, and many kids have combinations of both. These kids have major problems with transitions, and can seem oversensitive to the point of tantrums. Both my children have this, although my daughter to a lesser degree than my son. Find an occupational therapist trained in this disorder, and have your son evaluated. They will give you a questionaire about your son's behaviors. I don't know what area you live in, otherwise I might be able to recommend one.
Some books on this disorder are: Out of Sync Child, Sensational Kids, The Sensory Sensitive Child. A good therapist can help a lot. Even though your son is 4, don't count on the school district's OT to have a clue. Some school OTs are well-versed, and knowledgeable, but others are not, and don't even recognize this disorder. Please let me know if you need anything else, and good luck. It's not easy to live with a child with this, but once it's recognized, and you get some help and strategies, it makes life MUCH better.
Just wanted to add something after reading the other responses: Your son can have sensory processing disorder without having autism or Asperger's. It often is seen in combination with other disorders as well, like Down's syndrome and cerebral palsey. So don't get worried about that yet. ALSO, there are many pediatricians who don't know about this disorder, so don't leave it up to your physician. I've heard too many stories about parents KNOWING something was wrong with their child, and the pediatrician refuting them. In the end, every parent I talked to turned out to be right! I'm a teacher, and I have a student in first grade who is obviously Aspergers, but the pediatrician has never mentioned one word to his parents.