This condition is a normal temporary side effect, but if you had the thyroidectomy over a month or two ago, it may be a chronic disorder. during the course of a thyroidectomy (assuming it was a full thyroidectomy) as the gland is physically dissected away from the it's vesicular and neural innervation, the primary branches of the laryngeal nerve are carefully separated from the thyroid as to not be damaged during it's removal. It the nerve is damaged in any way during this process, it can lead to half of your "vocal cords" being rendered paralyzed , or nearly so. This leads to a raspy or horse sound to the throat, and is most likely a permanent condition.

You might take the optimistic approach, and realize that if both sides had been damaged, you would not be able to breath,and may not be here right now. Of another distinct possibility it that it could be an infection, but it would more likely present with some other symptoms such as a sore throat, coughing, phlegm, fever, etc. I think you should discuss it with your surgeon, or the doctor overseeing you for any surgical recover care. I wish you well!