I have Hashimoto's and it was undiagnosed for years. During that 15 year time span my TSH varied wildly from 6.60 to 4.87 two weeks later, to 2.75 seven years later, to 14.85 a few months ago. Hashi's has flares too; some times are worse than others until the thyroid stops working. If you think you are hypothyroid, keep getting tested. And like someone else said, get tested for thyroid peroxidase antibodies (TPOAb) as well as T4, T3 and TSH.
Good luck! Hope you feel better soon.
Acceptance is the key to happiness.
ITP - 1993
Celiac - 2012
Hashimoto's - 2012