Heavy and swollen breast

My left breast has been hurting me for the last couple of days. It feels very heavy and it feels as though it is pulling from below my armpit. I just did a self exam and think I may have felt something swollen, but I am not sure it if it muscle. It was located right where the armpit meets the breast (around where the bra cup sits). What can this be? Do you think it could be related to the fact that I recently gained weight and my bras are a little tighter? The other breast is fine…  Thank you for your feedback.

THE BREAST DOCTORS SAY:

It is common to experience heaviness, soreness or pulling pain in the breast, especially in the axillary tail area which is the part of the breast near the armpit that you have described. Ill-fitting bras do not provide appropriate support and can be a common cause of breast pain. If your monthly period is due soon experiencing these symptoms of breast pain and areas of breast swelling can be a normal result of hormonal fluctuations and these symptoms generally resolve after your period is over. However, it is important to ensure that your symptoms are not due to an underlying growth or tumour. Do consult your doctor should your symptoms persist.