Hi Suza, yes I'm hypothyroid, on replacement for nearly 3 decades, postmenopause & on HRT.
A TSH of 3.5 wouldn't usually be considered abnormal, but if you have not been tested since 2020 & you have symptoms, then please do ask your GP about testing again.
Reference ranges vary a bit between labs, but TSH at the lab I use currently goes up to 4.2.
Once diagnosed hypothyroid & on thyroid replacement, many of us need our TSH to be towards the lower end of the ref range to feel well (e.g. 1-2, especially young patients), so the suggestion of no higher than 3 you have seen mentioned online may refer to what's optimal for those with confirmed thyroid disease. That said, there is long ongoing debate about where the cut off should be for diagnosis. When I was first diagnosed, TSH ref ranges commonly went up to around 6.
There are quite a few other symptoms that would suggest your thyroid could be under-performing but some of the most obvious include fluid retention, constipation, weight gain, low mood, hair loss (inc outer 3rd of eyebrows), dry skin & poor memory.
I'm sure you'll have ruled out other possible factors for coldness & sluggishness such as eating too few calories, inadequate exercise, low weight, but metabolism does also tend to decline as we age.
https://www.btf-thyroid.org/thyroid-function-testsHope that helps.
Wx