I had my thyroid removed in 2016 because I tested positive for cancer. After surgery it was negative. I had them test again also negative. That is when all my heart problems begin. I developed AFIB and was taking to much thyroid medicine so the cardio version didn't work and didn't know I had to much medicine until after. Now on heart meds forever. Excessive weight gain. I was diagnosed with low blood sugar at 18. Now 62. So how does my body convert my T4 to T3. How does the medicine work different then my thyroid?