What Leads To Excess Fatigue And Lack Of Focus?

I am a 47 year old nurse. I have been working quite a bit but recently move 1 1/2 hours from my work. I work there 5-6 times a week. I am only saying this because my symptoms started after I moved. I am constantly tired, hard time focussing , I have noticed I urinate less frequently, I will fall asleep during the day (when I am normally very energetic ) I have become increasingly less interested in helping working with overtime. I am very dizzy and have to be carefree when I stand or move. I am 5 6 , 120, active normally, ride horses and now I do nothing except get up at 430 am and get home around 6 pm. I feel that there is something physically wrong with me (yes I understand the overworking) but is there something I should be checking on or should I give up my job I love so much. Also I should add that I have gained 10 pounds and I am working like crazy and watching what I eat??