I have two boys (5 & 6 years old now). The one went through terrible 2's starting at 15 months and ending at 3 years!!!! He is the happiest now and we have no problems. Except his eating habits :-(
You can look at his diet to make sure that he is getting all the vitamins he needs in the food he is eating. Lots of children are not getting enough vitamin B, which is a very important vitamin for the nervous system. Make sure he is getting enough calcium, calcium is very calming. When children are not getting all the vitamins that they need, they tend to get frustrated easily and cry easily over little things. A full belly, full of good nutritious food really helps with behavior and happiness. Take a good look at his diet to make sure that is not the cause.