Your fatigue/lack of energy is due to having 2 major surgeries in 6 weeks - at any age!
When I decided at 54 to have 2 hip replacements 6 weeks apart, my Mom, a veteran of many surgeries, told me not to do it. She was right - it took me almost a year to completely recover! I have tried never to do it again - in my experience, a single major surgery takes about 6 months of healing time - remember, surgery is an assault on your body.

So my advice would be to relax and heal - do your walking, therapy and as many daily activities as you are comfortable doing. Then kick back, read a book or take a nap, and let your body heal.
Sue