boobies

Is it normal for when you're about to start your period your boobs get kinda swollen? I told my boyfriend that they really hurt and he said they look/feel a little swollen. Is this them growing or is it period? When I felt them I felt something hard. I'm 15 years old and I can't be pregnant. I don't know what it is. Ive had sore boobs before but never these hard things I feel, and definitely never this sore.