I felt the same way during my recovery. Others were posting about all the "normal" things they had resumed doing, and I was still tired, weak, months after my Sept. 2015 surgery. When I posted about it (as you have done), readers rushed to assure me that I could not measure my progress against that of others. That assurance helped my mental outlook tremendously, and went easy on myself from that point forward.
That said, my recovery was very gradual. Although I returned to work at 8 weeks, I'd guess it was at least six months (probably longer) before I felt somewhat back to normal. I was 61 at time of surgery, and very out-of-shape. I had 12 weeks of cardiac rehab and that helped somewhat.
I think in my case, I feared doing too much, worrying that I would tear something, pull something, break something. I was NOT fragile but I felt as if I were. Part of the problem was that I live alone with few close friends so I dwelt on my condition more than was mentally healthy. Coming to this web site really helped me retain perspective.
Hope this helps.
Hugs,
Michele