Just Kind Of Currious As To What Could Be Getting

Just kind of currious as to what could be getting me all the attention? Pretty common for people to remar or ask if I'm feeling all right . I do feel tired often even though I do average 8 hours of rest. I had thyroid cancer 15 years ago and complete thyroid was removed. I'm on synthroid and I believe they intentionally keep level sitter low ! ,I think it helps to prevent reaccurance or return? Not sure if this would do that or not? Anyway any ideas what would make someone feel like that? I'm pretty active and do run and lift weights in cycles also. Thanks. John