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

I had both knees replaced at Mayo Phoenix last year 3 months a part. I am a super active 73 year old. I experienced a little bit of the same things you are feeling after the second surgery. Surgery does a number on your body. It is traumatic to your system. I give blood at the Red Cross about every 8 weeks. When I went in about two months after surgery, my hemoglobin was lower than their policy allows for blood draw. I was surprised, but that was the reason for being a bit lethargic, workouts were not as aggressive, I tired more easily, had a bit of low stamina. I was anemic according to the numbers. When I discussed this issue with the fine doctors at Mayo, and after reviewing if I had any other trauma or blood loss, they suggested I CAREFULLY take an iron supplement and that . Too much iron can be dangerous. In Arizona you can schedule your own battery of blood tests without a prescription. I think the hemoglobin test was $25.00. I did it to double check what the Red Cross numbers indicated. It was low: 12.1. It should between 13.8 and I think 17. Even with taking the iron supplement, it two more months to get it to my pre-surgery level of 15.2. Talk to your Doc. This may be what's happening.

I had TKR on my right knee 10 weeks ago. My knee is recovering well, still some pain due to the intense PT. But yes, I feel tired every day. After doing a daily task like making breakfast or taking a shower I am exhausted. Have to sit down and rest. I understand fatigue is common after surgery, so I am not worried. But it is so frustrating to have limited energy. We must have patience and give ourself permission to rest so the body can heal.