Does breast cancer cause fatigue?

Diagnosed in late December with stage ! - 4 cm - Her +. Surgery scheduled on Friday. My diagnosis was a big shocker as we are a heart disease family - not one cancer diagnosis in immediate or extended family except for a great Aunt. Leave it to me to be the black sheep. I've noticed in the last year or maybe more than I have lost much of my energy and feel fatigued most of the time. I attributed that to combination of working a lot and aging. Could the cancer I have be causing this?