As a man, my opinion should only be taken lightly, so don't worry about what I'm about to say.
I have 2 gripes about big breasts. I get some people like big boobs, and more power to them, but bigger isn't always better.
First, it's not physically healthy to have too large of breasts:
"Disproportionately large breasts can cause both physical and emotional distress for patients. Patients with macromastia may experience physical discomfort resulting from the weight of their breasts. The resulting pain can make it challenging for some patients to perform common physical activities. Along with the physical ailments of macromastia, some patients may suffer from emotional distress or more significant mental health problems as a result of their large breasts."
-American Society of Plastic Surgeons article on breast reduction surgery.

Second, the desire for large breasts is a body image problem. I don't like that society still favors unreasonable expectations on one's appearance. I encourage liking the body you have and not listening to peers who suggest otherwise. While I encourage having a healthy body, and work to manage issues like obesity, I also encourage being confident in the body you have. You shouldn't change it if it's in good health already, and you shouldn't change it just to look good for someone. Your body is your's alone, and feeling good about your own body is good for your mental health. Don't let body image affect the way you feel, and don't feel bad about the breasts you have.

That being said, there is a health risk to having large breasts, and if you don't feel physically comfortable (ie, your back hurts), then consider the options available that are made to help improve your physical health.

Finally, if necessary, consider surgical removal of your breasts entirely, as people with a family history of breast cancer stand to significantly reduce the risk of developing it themselves after having their breast tissue removed. Your health matters more than appearance.