Weakness in the lower back and joint pain in anaemia are usually due to low haemoglobin, which reduces oxygen supply and causes fatigue and body aches. Eat iron-rich foods like green vegetables, dates, and jaggery, and include protein foods to help improve strength and recovery. Take proper rest, stay hydrated, do light activity, and avoid overexertion while your body heals. A doctor can check your levels and guide you to suitable supplements and treatment to improve your health safely.