Although it sounds like a hormonal thing I would have it checked out .... GYN would be a good place to start. I would NOT however worry about a return of your skin cancer .... it doesn't work that way as a rule.
I totally agree with tresa47.
Please..please...please call your gyn or primary care doctor and let them know what is going on. Any kind of lump or thickening in the breast is nothing to fool around with. It could be absolutely nothing or it could be something . The quicker you get this checked out the better. Please make sure you get the answers you want...make sure your doctor addresses all of your concerns...please check back and let me know how you make out...my prayers are with you....