hello madam ,
As ur symptoms and blood reports of thyroid indicates u had symptoms of hypothyroidism
as it is treated by the GP. Per se hypo thyroid (low thyroid ) not causes change in voice . But ur symptoms got reduced after increasing the thyroid hormone replacement
seems u had low thyroid hormone secretion .
Yours is a long standing case of hypothyroid and change in voice is a significant function abnormality
, better to go for USG NECK and USG GUIDED FNAC , so that we can evaluate completely regarding the pathological nature and the size of thyroid gland and helps in further course of treatment and prognosis of ur disease .
Hope u get through these investigations and have a favourable report