Mood swings

I try very very hard to be understanding, but, there are times that my oldest son’s moodiness drives me insane!!
Sits, head down, won’t look at anyone, won’t take part in conversation, won’t even say what he wants or if he wants to eat. But, yet, if I ask him what’s wrong, he tells me, ‘Nothing.’ And I cannot get him to talk at all. Especially when 30 minutes before, he was exact opposite – talking, laughing, joking….