Hi.
I understand what you are going through.
A breast cyst can increase in size after several months. That is the reason why patients are advised to perform self-breast examination, in order to check for any changes in the character of the cyst (like increase in size, presence of associated symptoms, etc.) There are also cases when the cyst regresses in size after several months.
I agree with your decision to have the mass removed. The specimen will be sent to the pathologist for evaluation.
Good luck and stay positive.