I need energy, and I feel tired all the time. What can I do?

Weakness. multiple causes can result in weakness have your primary physician do a complete metabolic workup that should also include thyroid function tests; also maintain good sleep habits, proper nutrition, increased exercise, yoga.
Feeling tired. I would make sure you're eating a healthy diet and getting at least 7 hours of sleep nightly. If despite these measures you still feel tired all the time, I'd get a checkup with your doctor to elucidate the cause of your chronic fatigue.