Why is my right breast shrinking?

Your hormones may still be on the proper cycle, but you are producing less estrogen then you did at age 20. This is a natural phenomena and is the main reason breasts shrink. Exercise, diet and weight loss can also influence this. There are many implants available to correct this problem. The oldest patient I have done a breast implant augmentation on was 69, replacement on patients as old as 81. You are not to old.

Many variable can affect breast size. Age, hormone level, weight, etc.. are just a few. Best to be seen in person to determine what can be done if you want fuller breasts.