Is my thyroid burning out?

[zhunt]

In 2014, I suffered acute subacute thyroiditis (DeQuervain's thyroiditis) at age 27 that sent me into a severe thyrotoxic/hyperthyroid thyroid storm. I was hospitalized and lived through it. I had RAIU + scan, ultrasound and labs that were all diagnostic of subacute thyroiditis, and negative antibodies for Hashi's and Graves.

In 2015, I experienced what felt like a few more thyroiditis flares, but in general, my thyroid levels went down to low-normal ranges and my TSH rose to normal-high (hanging out around 3.0 - 3.6, with a reference range of 0.36 - 3.74 uIU/mL).

In 2016, I turned 30, and I began to struggle with weight gain for the first time in my life. I'd always been kind of, unusually skinny, but in 2016, that all changed, and I dealt with other hypo signs, such as chronic constipation, low body temp, hair falling out in the shower and fatigue. My eyes became puffy almost overnight! But my doctors just kept telling me, oh, you're just getting older, your metabolism is slowing down. Personally, I disagreed; I eat healthy, I exercise, I'm naturally underweight.... not overweight. I didn't complain much because I was just glad to not feel thyrotoxic anymore. I continued to get my TSH and FT4 monitored every 6 months. I've become so ill in general though, that I haven't been able to work. What a great way to end your twenties.

Now, here we are in January 2017, and my TSH is just now starting to test outside of range:
1/27/2017:
TSH
4.220 uIU/mL *H
(Ref: 0.36 - 3.74 uIU/mL)

FT4:
0.92 ng/dL
(Ref: 0.76 - 1.46 ng/dL)

My FT4 has been much lower than this, but still "normal" with a TSH that was within range around 3.0. Endo wants to re-test in 6 weeks and if my TSH is still low, start me on treatment. If it's still bouncing around, he'll continue to monitor it. He keeps testing my antibodies for Hashi but they always come out negative. Could this change, or is my thyroid just failing now? Anyone else experience their thyroid dying after subacute thyroiditis? I'm also concerned about treatment. I'm very sensitive to hormones - I get anxiety so easily. I'm rather afraid of Synthroid and won't even consider NDT because it's T3 and that can be even more stimulating. I've also heard there are issues with generic synthroid (levothyroxine) not working very well and people going on Synthroid brand name again but don't know if my insurance would cover it.

Thank you!