Hi,
I was exactly the same. It took a year to get my TSH right. Like you I wasnt ever really very underactive. I reckon I have been getting more underactive over time, and it has coincided with me sytarting thyroxine.
Go back to your GP. Tell him/her how you are feeling. I also felt perky for a few weeks every time they upped my dose, then it felt like my body got used to the the levels of thyroxine and slowed down again. My main symptoms were 'cant be arsed' with anything. Some days I 'couldnt be arsed' to get up, and so would have to phone in sick to work. When I told my GP that, he seemed to listen.
I am now on 150mcg, so I must be fairly underactive after all.
A tip for when you are getting your bloods done to test your TSH/free T4. Try to get an early appointment and dont take your thyroxoine until after you ahve had blood taken. Dont know how mkuch of an effect this has, but my osteopath (she's into thyroid help groups etc) told me. I was certain that I neede a higher dose of thyroxin, but when I had been tested, my TSH was very low, so my GP said I was on the correct dose. However I still felt rubbish, so went for another test, but this time didnt take my thyroxine in the morning (my bloods were at 9am, and I take my meds at 8am). My TSH came back as being just within normal, but high enough for my GP to take notice that I could do with a higher dose.
I hope that all makes sense! I dont know if thyroxine levels are highest straight after taking the tablets, but uit is worth a try?!
Ch