During thyroidectomy surgery, you get a flood of hormone as they remove the thyroid, which is why they sometimes delay the start of synthetic hormone for a few days. That is why you felt good for the first two weeks until that influx of hormone wore off. They do calculate initial dosing by weight as a starting point, but everyone is different. All sorts of things can affect absorption of levothyroxine, including PPIs, like Prilosec, and your body’s requirements change a bit daily and seasonally but once you reach your optimal dose, any minor variations will not affect you. I dont know much about Cytomel except I think you can eat after taking it but you do need to wait an hour before eating on levothyroxine, and that includes drinking coffee. Give it some time. Once your dosage catches up, you will be fine. I personally keep my TSH between 0.5 and 2. You will know where you feel best.