I do not want to alarm you. I am a big believer in mind power. Sounds kind of jerky but I do believe that how we think really effects of health. That said, I took cytomel while on synthroid. I had a bad reaction. But I am only one person and am on a very high dose of synthroid.
I am also not as quick as I used to be to blame the first thing. I usually try a new med more then one time to be sure that it is the problem.
That all said, and so I don't scare anyone out of taking something they may need. The reaction I had was some disorientation and feeling slugish. Nothing terrible.
T3 meds may help you as Cytomel - but as your doctor stated you may need to balance the thyroid first. T3 can also help with that IF you and your doctor decide that may be good. It is taken along with Synthroid.
Also a T3/T4 med is good too - Armour is a T3/T4 natural combo from dessicated pig glands and assists hypo patients as when their own thyroids worked on their own.
Which ever you and your doctor chooses is the best plan - Keep track of your progress on whatever you choose to try.