Parenting

First I would ask if there are any sudden emotional changes in his environment?  From the way you posted, I quess you are a single dad.  Children display their emotions through acting out, crying, or becoming anti-social with other kids for instance.  In your case it seems as if he wants attention and a lot of it.  When he cries you immediately try to see what he wants right?  This is the attention he is searching for.  Although, kids are smart too.  They think crying will be the remedy for all things they want, so don't be fooled.  You are in control of what they need and you are in control of what you deem him to have also.