The same thing could happen if they had decided to switch you to a different brand name as well. I have read indications the level of levothoroxine is higher in Synthroid than in the Levothroid I take, for example.
The generics get the same scrutiny from FDA as the brand names, but one generic is not equal to another generic either. Hence, your doc could finally get you leveled with the generic you are getting now, then you get yet another generic and have to start all over again. The only way to avoid that is to get the doctor to put his foot down and order no switch. Then you hope the insurance company will pay their share.
I am fortunate in that respect. My insurance covers Synthroid or Levothroid and the pharmacy (it's an HMO) will not switch without a doctor's order. Although the cost to them may vary, I pay $15 for 90 pills, no matter which brand my doctor prescribes or what strength.
Products such as Armour are not covered at all, however, so those who want that sort of treatment would need to go elsewhere and pay full price.
You can read what the American Thyroid Association has to say about switching thyroid brands here: http://www.thyroid.org/patients/Qand...thyroxine.html