Fever for three days with nausea, headache, joint pain, loss of appetite, and weakness is often due to a viral infection, such as the flu or sometimes infections like dengue or other seasonal illnesses. These conditions can cause body aches, low energy, and fever. Take rest, drink plenty of fluids, and eat light food to support recovery. As the fever has lasted for a few days and has multiple symptoms, consult a doctor to confirm the exact cause and treat it properly.

Full body pain with weakness and breathing difficulty could be due to a viral infection, anemia, asthma/COPD flare, or other medical conditions. Check your oxygen level if possible and seek medical care promptly if breathlessness persists. Stay hydrated, rest well, and avoid self-medicating until properly evaluated.