It's most probably infatuation than love. Like Peter said it's normal to go through such phases when you are young. Right now, you probably are experimenting with your feelings towards people of opposite sex and will eventually figure out what love is. Love has one important component called commitment. When you see through that, you'll stick to your love, hopefully forever.
So there's nothing wrong if you are switching girl friends. Just make sure that you aren't caught between the two and that you are not spending away all your savings on the girls
