So, something my boyfriend and I like to do is have rough foreplay, it doesn't hurt at all. But he was extra rough with my boobs this time and they've been a little sore since, though today I woke up and my left boob hurts a lot more than it did yesterday (when I'm up and gravity is pulling on them they hurt, when I apply pressure they hurt,). It could very well be also be the way I'm sleeping because I lay on top of them. I always think of when my older sister would say her nipples hurt because of breast feeding. Why is this happening? Should I be worried? Why is only one nipple hurting and not both?