I don't understand why your doctor would recommend thyroxine...... that's used for hypothyroidism (i.e. when the thyroid doesn't produce enough hormones). You have hyperthyroidism, which means your thyroid produces too much hormones.
Hyperthyroidism can be very dangerous to your health, if not treated properly. It can cause heart problems, contribute to osteoporosis, cause weight loss, etc.
Have you been on a thyroid replacement medication? If so, you're over medicated.