There are a lot of things going on other than just toxins that will effect your thyroid.
As I mentioned, overstressed adrenals may be the primary one. Our lives are typically filled with stress and it is getting worse. Modern music is very stressful, especially when compared to classical. The rock/country beat hammers on our adrenals. The TV is overstimulating as it tries to gain your undying attention. Stimulants such as caffeine and energy drinks wreak havoc. Work, family, and all other sorts of obligations can pile up. This slowly over time taxes our adrenals. The adrenals are tied to our thyroids. Without healthy adrenals, you CAN NOT fix your thyroid.
The TSH means nothing. You shouldn't think about the TSH.
If you have a doctor that revers the TSH, you should find another doctor.
TSH is the FEEDBACK LOOP. When you are supplementing your thyroid the feedback loop means nothing because you are externally stimulating the system.
It's like this. Imagine that your TSH is the speedometer on your car. Your goal is to drive down the freeway at 55 mph. But your car is broken, so it is on a trailer being towed. What does the speedometer say (the feedback loop)? It says zero. What are you actually going? 55!
Its the same thing for TSH when you are supplementing. It means nothing at all. It is actually a dangerous distraction for doctors that don't understand basic control system theory, which is what your thyroid TSH is part of.
If your mechanic was sitting in your car as it was being towed down the freeway in the above illustration and was fixated on the speedometer and was upset that it said zero, you would fire him, wouldn't you? He would be a complete idiot. So are doctors that don't understand TSH labs. What's worse is that they are typically unwilling to listen and learn from their patients.
Focus on the free T3 and T4.
If you are interested in learning more, this is probably the best website: