Breasts have started to enlarge. Could it be exercise, vitamins, medication, etc?

I am 31 years old and had been pretty consistent in breast size. I noticed earlier this year that my breasts have started to enlarge. I have gone from a 32DD to a 32/34H. Could it be exercise, vitamins, medications, etc. that could be enlarging my breasts or another reason. Most doctor tend to say I am off my rocker when I say I feel that magnesium is causing an increase, although I do not think it is the only thing.