Not sure what the doctor expected from your switch to Synthroid. Perhaps a slight difference in absorption????? Also, 14 days is not long enough to evaluate a change in T4 med dosage, much less just a change in Brands. I am not very impressed with your doctor at this point. What is your daily dosage of Synthroid. What were your latest thyroid related test results and reference ranges shown on the lab report? Even more important than lab test results are symptoms. Please tell us about all the symptoms you have.
I agree with what gimel says and would also like to know who says you're "too old" to switch to Armour and what heart contradiction there might be.