For 3 weeks, i have had constipation, bloating, gas, distended abdomen, nausea, headache, extreme fatgue, dizziness. tested & not pregnant. advice?

Need more info: Any fever? Have you started any new medications? Are you sleeping well? Have your blood cell count, liver and kidney and thyroid function checked by a simple blood test., for additional clues.

Change diet: Try to avoid fried and fast food and alcohol and take in more leafy greens and non processed food. Try some exercise like walking. Consider getting a mono test and if persists see a doctor.