My face seems swollen what is it?

my face is usually thinnish but not bony. but now just when school started it seems like i was sleeping down hill. i thought that was the case so i propped up when i went to bed and my face was still puffy all day long. what is this? dose heat make your face thinner? dose coldness make your face puffyer? i haven't gained any weight. PLZ HELP! THANKS