What Causes Severe Fatigue And Stiffness In The Muscles?

Hello, I m 47 year old female, with a semi-active type of job as a claim processor. My chief complaint is I m chronically tired, no matter how much sleep I get. I NEVER feel refreshed, yet if I m outside doing yard work which I love, I could keep going and going for hours. But then once I m done and get cleaned up, I m really exhausted. If I spend a day playing actively with my small nephews, I m wiped out the next day! I ve been having muscle stiffness more and more despite trying to excercise moderately at least 3 times per week. If I go more than 4-5 days without trying to excersicise, my body feels as if I ve NEVER worked out before. I also have been diagnosed with ADHD, and take 40 mg of vyvanse mon- fri under a Drs super ion, along with 40 mg of citalopram ea day. I probably should mention to my 67 year old mother has scleroderma and fibromyalgia. I m worried I could be inheritating her illnesses. Any advice would be much appreciated about this.