Hi there,
This pain,including swelling in one or both breasts, could very well be related to hormonal fluctuation with respect to your menstrual cycle.
Pain can be due to many benign causes,(including pregnancy) and it's rarely associated with cancer,particularly if the pain occurs in both your breasts.Fibrocystic breasts condition,breast infection,oral contraceptive pills,tight clothing could cause similar pain.
Avoiding foods and beverages containing caffeine, such as coffee, tea, chocolate and soft drinks, can decrease water retention and may help to alleviate the discomfort.
For the time being,you could take some over the counter pain relief medications,but if the pain still persists after your period is over, you would need to see your doctor for a detailed clinical examination.I really doubt that your problem is a serious one,however it's better to make sure, so you can find out the cause of your breast pain.okay?.
Best wishes and I hope you feel better soon.....