It would be best to get a follow up with your breast specialist and get a proper clinical evaluation done.
If the cyst is painful, talk to your doctor about removing the cyst fluid. The fluid can then be sent for lab analysis.
The pain could also be due to wearing tight clothes, trauma or pressure to the site. Try OTC pain relief medications and see if they help.
Do let us know how you are doing and what your doctor advises.
Hope this helps.