How would i know if i have an underactive thyroid?

Blood test: You MAY feel sluggish, gain weight, have hair thin or fall out, feel a fullness in the front of your throat. These are all late findings and pretty inaccurate. Best to check with a doctor who can order some blood tests and find out much more accurately

Thyroid lab tests : Low thyroid function causes low energy, constipation, loss of hair, weight pain, puffy face, muscle pain, irregular menstrual periods