Firmness of the breasts is a capsular contracture
From your description you most likely have a capsular contracture. This is causing the firmness of your breast. If it is causing you pain or a change in the shape of your breast then you should be evaluated by your plastic surgeon. You may need to have a surgical procedure to correct this problem.
You may have developed a capsular contracture and you probably need to be seen by your surgeon to be properly evaluated.
It is difficult to know for sure without an examination, but it sounds like you may be developing capsular contracture. Seek consultation with a plastic surgeon so that they can examine you and give you the most accurate answer possible as well as a treatment plan. Best of luck.