The thyroid gland regulates your metabolism. An underactive thyroid (Hypothyroidism), the most common cause of fatigue, means the gland produces too little hormone, leading to symptoms like tiredness, weight gain, feeling cold, and depression. It is treated with daily hormone replacement pills (like Levothyroxine). An overactive thyroid (Hyperthyroidism) means it produces too much hormone, causing anxiety, weight loss, rapid heartbeat, and heat intolerance; treatments include medication, radioactive iodine, or surgery to slow down hormone production. You should consult an Endocrinologist for a precise diagnosis, which typically involves blood tests at any major diagnostic lab or hospital. The cost for tests and generic medication is generally low, often between $30 to $100 for initial testing and $10-$25 per month for pills. Long-term management involves taking medication consistently, having regular blood tests to monitor levels, and communicating any new symptoms to your doctor.