I'm pretty constant now. The right mix right now is one dose 5 days a week, then a higher one on weekends. For a while, I was like you and my dosage would fluxuate every couple of months.
Make sure you are taking your synthroid at least 2hrs after a meal and an hour before you eat anything else. Also, don't take iron anytime near it.
You may also want to try taking it with distilled water. I have to do this, as something in the water was probably affecting absorbption of the synthroid.
Ghost of BYU- You miss the boat on this one. It's not akin to taking testosterone b/c your testosterone levels are low or anything like that.
For example, in my case I have Hashimoto's disease which basically means that my immune system is attacking my thyroid gland. Is there something wrong with trying to fix that?
It's performance enhancing in the same way that taking antibiotics is when you have some sort of infection.