This is not uncommon at your son's age, so don't panic or feel isolated.
I would try the reward system. If he comes to you when he needs to have a diaper change, he gets a (meaning ONE) M&M. If he gets up one the table with out screaming or having a temper tantrum he gets a M&M. If he lays still while the dirty diaper is taken off he gets a M&M. If he lets you clean him up and does not kick and scream he gets a M&M. If he does not kick and scream while you put the new diaper on he gets a M&M. You can try other things like skittles.
At his age break up the steps into minute bits of acts. This should be done with no threats like, "if you don't lay still you won't get your M&M." Instead you say at the beginning you say "When you come to me I will give you a M&M." Once. Then after he does you can say "Wow. You did it." And so on with each task.
The reward system is harder than any other system because you can not loose your temper. If you must scream, go out side and scream--my daughter chased me into the shower one time.