I have multiple personalities?

If you're just expressing your emotions at the time, it's completely normal. It's not multiple personalities, though. It's just different moods. When I feel depressed I like to wear jeans and long sleeves and listen to 90's grunge, but when I'm in an upbeat mood I like to listen to newer rock and wear shorts and a T-shirt. Trust me, you aren't a poser. It's normal.