What does these smileys mean?

[Soren]

-_- can be either tired or disappointed. Usually disappointed. Like if you were sighing or saying "ugh..."

-.- is essentially the same thing

X_X is dead. So if someone is stressed, they can use this. Comedic, like a cartoon character with X's for eyes. "Bleh, I'm dead!"

v.v is like the first one. can be tired, but usually means someone with their eyes closed in disappointment.