I take Liothyronine (Cytomel) too. My T3 hormone was way too low. I could barely get out of bed for years, until a specialist corrected this after a full thyroid blood panel - and someone who knows how to accurately read the T3, Reverse T3 and Free T3 results. Synthroid contains T4 ONLY. It does nothing to replace missing T3. I have mine specially compounded with a slow release formula at a compounding pharmacy, so it lasts longer. And instead of Synthroid, I take Armour Thyroid, as it contains both T4 and some T3.
Even so, I take the two thyroid meds at separate times, about 4 hours apart, along with a natural adrenal supplement, again at a different time. All three of these spaced out throughout the day are what keeps my energy up all day. I can NOT take them all together, even if I was ordered to, as they would cause heart arrhythmia.
Four hours after my last dose, I take calcium or iron.