Cysts can cause pain in the breast. The amount of pain you feel is not necessarily correlated with the size of the cyst but with how full the cyst is. A small cyst that is full of fluid can be more painful than a large cyst that isn't as full. Try staying away from caffeine and if it is due to a cyst it might get better. Occasionally a cyst my need to be drained by inserting a needle and drawing out the fluid if it is very painful or very large.