What Causes Excess Tiredness Inspite Of Having Normal Blood Test Result?

I am 57 years old. I am usually very very energetic. I usually do Zumba classes 3 times weekly. Lately I am doing 1, because I am so tired. I got my blood lab work, and everything came out very good. Today at work I could barely walk by the end of my 8 hour shift. I usually get b12 shots for energy, I got my last one 2 weeks ago, and I guess it didn t work. I had a total hysterectomy in 2013. I have never taken hormones. I am taking phendimetraz to help me with my weight. I am taking alaprazolam, because sometimes I feel stressed out at work. Th doctor gave me .50, but I take 1/2 a pill, and only when I work. My daughter has lupus, hoshimoto, thyroid, renauds. She has been telling me to get checked. But since I hardly ever get sick, and I am so active, didn t think much of it.