Low TSH & LOW T4

I have had chronic fatigue and various other symptoms of hypothyroidism for many years. I finally got tested for more than my TSH (was tested before for just that and was in the "normal range" so the doctor did not look further). For the last six months my brain fog has gotten so bad I often can't find a word mid sentence. I feel like my synapses just are not firing right.

Here are my levels:

Free T4 0.9 (reference range 0.8-1.8 ng/Dl)
TSH 1.59 (reference range 1.59 - 4.50mIU/L)
Free T3 2.4 (reference range 2.3 - 4.2pg/mL)

As you can see I am on the low end of "normal" but I can tell you I am feeling horrible and something is very wrong. My Estridiol, FSH and ovarian reserve are all great at age 40, as of testing from a couple months ago.

I know that having both low Free T4 and Low TSH can mean something is going on with the pituitary and/or the hypothalamus. Can anyone give me some insight into this? My next step is to get the two antibody tests for the thyroid, so if I can possibly rule out hashimoto's, if there is a weird chance that I have it, since I have all the symptoms.