Exercise / Healthy Diet after BC

I was and am overweight and had a very stressful time with my father maybe eighteen months or so before I was diagnosed. At diagnosis I was very happily retired enjoying my life with my husband, family, friends, dogs and my quilting.  I have wondered whether the extreme stress with my father contributed to my cancer, or was it simply my fault for being overweight or just bad luck.  I had mastitis with my first baby.  I didn't take the pill for long and never took HRT. A light drinker most of my life.  An intermittent excerciser.   I had a benign lump removed from the same breast that got cancer many years ago.  It was always a lumpy breast.  I used to check the lumps there but ridiculously didn't find the lump of my cancer, now wish I had found it earlier.  Thank goodness for Breast Screen Australia and regular mammograms.  No family history of BC.  I feel guilty about my weight. What overweight person doesn't?  But thin fit healthy eating women can get BC and all the overweight women out there don't all get it, just some of us.  I don't suppose I will ever know why I got it.  I will die a long time in the future I hope without medical science solving that conundrum.  My oncologist said, the main causes of BC are being a woman and age.  I am glad he did not lecture me on my weight.