I am a 43 year old female with unilateral thyroid enlargement. Been obvious for at least 6 months. Am absolutely terrified. Any advice?

Don't worry. See a thyroidologist to determine why one side is bigger. Is it a nodule or cyst? Have him/her check it out.
Don't be terrified. Thyroid nodules are overwhelmingly benign. And worst case scenario, thyroid cancer is extraordinarily treatable and survivable, especially at your age. If you have a thyroid nodule accounting for your enlargement, you may need to get a fine needle aspiration to tell more.