I would also suggest further testing on the pituitary.
What are the lab's reference ranges for the FT3 and FT4? Different labs use different ranges, so it would be helpful to know them, even though you say they are "low".
I'm sorry, I don't know what an Anion Gap is so I can't help you with that part, but with your Free T's both low, I'd say you are hypo. TSH is a pituitary hormone and is not totally indicative of thyroid condition, even though a lot of doctors swear by it.
Have you had any antibody tests done to see if you have an autoimmune thyroid issue, such as Hashimoto's? I'm learning that low vitamin D is quite common with hypo/Hashimoto's. What, if any, symptoms do you have?