I find it not unusual for kids--especially young ones--to have cranky periods at the end of the summer (tired from "too much" play, transitioning into school--in this case maybe his first real school experience?), or, as you suggest, during a growth spurt. Putting a little more routine back in his life, with emphasis on sleep, is probably a good place to start from. Also I have found that I have to remind myself not to come down excessively on lying/making excuses, as it shuts down communication, and makes it difficult to find out what's really happening. ("We will love you no matter what you do or say. We need to know what you really think/said/did/saw/experienced so we can do our best to help make the situation better.")
