What Causes Low T3 Level Despite Taking Thyronorm?

Hello Doctor, My mother (aged:60yrs) has been taking medicines for BP and thyroid since around 5 years. BP tablet. - Cardace 5mg Thyroid tablet - Thyronorm 75 mg/50mg Recently, she has been complaining fatigue symptoms (getting tired more often while doing normal household work). We did her CBC,T3,T4,TSH, B12, Iron, Renal profile and liver function tests. 1) I would like to know the reason for her low T3 levels, and how can it bring it to normal level. 2) Also, does she has low iron and b12, as they are just above lower permission value. 3) When consulted doctor, they mention her thyroid is OK..but after reading about importance of T3, I m little concerned about her. Please suggest how to improve her T3. 4) does her low T3 and B12, iron and haemoglobin levels are related to each other ?? Summary of her report: -------------------------------------- T3 total- 0.75ng/ml. (Low level?) T4 total- 9.27ug/dl TSH- 3.46 uIU/ml Vitamin B12 (serum) - 181 pg/ml Ferritin (serum) - 39.6ng/ml TIBC (serum) - 320ug/dl Iron (serum)- 56ug/dl Transferring saturation (serum)- 17.5% Haemoglobin - 10.4 g/dl Renal and liver function test reports are all perfectly fine. Thanks -Sandeep