J.H.
I agree with what some of the others are saying; I think this might be his way of looking for attention from you. He had you all to himself, and now he has to share! When a child that age gets upset, a lot of times they don't remember that they can tell you how they feel, and they revert to crying, because it gets the desired result. I think if you set aside some time (even 10-15 minutes a day) to do a fun project with him, you can talk to him in a positive environment about why he gets upset and cries. I've found with my son that if we talk about a tantrum after the fact when he's in a good mood, he's way more likely to use his words to tell me what happened to make him upset, and we can talk about different ways of handling it the next time it comes up. Hope that helps you! I'm no expert at this either--just taking it one day at a time!