Severe discomfort in the joints of the legs and back can be due to causes like muscle strain, arthritis, vitamin D or calcium deficiency, or prolonged sitting or standing. You can take rest, apply warm compresses, do gentle stretching, and use mild pain relievers if needed. Ensure a healthy diet with enough calcium and vitamin D. If the pain is persistent, worsening, or associated with swelling or stiffness, consult a doctor for proper evaluation and treatment.