The swelling is thought to be due to fluctuations in the circulating level of hormones such as oestrogen and progesterone. ( A Change in your hormones)
Dietary changes that have been found to help sufferers – a low fat, high carbohydrate diet, reducing the amount of salt intake during the pre-menstrual time and reducing caffeine and alcohol intake.
Trying to reduce stress, increase aerobic exercise and getting adequate sleep have been advocated and are undoubtedly good lifestyle measures.
I get exactly the same thing, don't worry. Have you had a breast u/sound?? If not go to your doc and tell her whats going on. You could have Fibroadenomas ( non-cancerous lumps). They are very common in young girls. If it's not that you may just have fatty nodules, breast tissue in young girls is always changing and can cause this. This also can be very painful, i have both! Don't be scared when you hear "lumps" 80% of the time they are harmless, in saying that though it is important to have reg check ups and do your own breast examinations :)
Oh almost forgot! Evening Primrose can help with breast pain, you get it from health food shops.:)