You need to. Begin brand name T4 replacement, and have your doctor check your levels every six weeks until they are normal, and then once / year. You will be on this medication for the rest of your life. Don't believe internet scams about the thyroid. Trust your doctor.
Hormone replacement? If only half is removed then 80% will be ok and produce enough hormone from the half that is left. About 20% will need supplementation. If the whole gland is removed, then you will need supplementation. I agree that most are easy to supplement, but others need several dosage changes to get the amount right. Be patient, it can be helped.