Pain behind the knees when standing may be caused by muscle weakness, joint strain, circulation issues, or knee problems like arthritis or fluid buildup. You can relieve it by taking short breaks to sit, doing gentle stretching and strengthening exercises for the legs, and wearing supportive footwear. If the pain persists or worsens, please consult a doctor for proper evaluation and treatment.

Feeling constantly tired and unmotivated may be caused by stress, depression, poor sleep, or nutritional deficiencies. It is best to consult a doctor for a check-up and possible blood tests to identify the underlying cause.