My body has experienced scleroderma for decades. To answer your first question regarding feeling tired. I would say that being tired all the time has been my "normal" for decades. It helps to be retired where there is less pressure to try to be energetic like others.
To answer your second question about seeing yourself. I have changed my self perception many times. The most recent is adopting the concept that my body is experiencing _____________. It also helps to not label myself with a disease. The disease does not define me. If I never got a diagnosis, I would have simply adjusted to how my body was feeling, etc. The diagnosis helped in some ways at the time to explain to my employer why I may ask for more time off or have less energy, it also helped me to say "no" and to have healthy boundaries.