I Am Female Who Has Survived Breast Cancer But No

I am female who has survived breast cancer but no one can tell me how to help me with why I have shortness of the breath when I am walking. I have had thyroid removal & 3 rods insert in my back. I am in constant pain the worst part is the shortness of breath . I can't even walk far enough to exercise--- and I have been told to lose weight. Not the issue I have had this problem for well over 10yrs. even when I was a size 8. now size 14/16 after throid surgery. Help me please.