247brain fog, dizziness, constipation, weight loss, tiredness. Ct of head chest abdominal MRI head CBC thyroid o2 tests all normal. What's left? I'm 25

Sleep. How is your sleep? If you have a significant sleep disorder, it can cause some or all of these symptoms. Consider a sleep eval if nothing else is found.
Treat constipation. You may take a fiber laxative like Metamucil and drink enough water daily so that your urine is colorless. For the long term you may try to increase your intake of fiber foods. Consult this site for fiber foods.