When do you go on medication-subclinical hypothyroid

hello,
my last two blood tests have come up subclinical hypothyroid and my result
was 4.1 out of 0.38-5.5 mU/L, and it says that 3.5- 5.5 could be subclinical- should I be
on thyroid medication and if so, has anyone heard of Naturethroid ?
Is thyroid med something that once you are on, you can't go off?
thanks