hi chez -
well, i'm a guy so there will be some limits to how this maps over, but anyway, here's my go.
at age 20, i started noticing more and more fatigue. i'd been in tri for over 5 years at that point, and knew my body very well. i was performing badly, recovering slowly, and even after 10 hours of sleep at night i'd need a nap after breakfast. the student clinic wrote it off as "exam season flu." the sports clinic were on it, and noticed my thyroid was the size of a melon. some bloodwork, and i was diagnosed with hashimoto's disease.
i started in right away on .175mg of synthroid. the dose has changed many times since and 10 years later i'm now on .125mg - my lowest ever.
as the others have said, hormone changes are SLOW changes. adjust the dose tomorrow and it's weeks/months before blood levels settle in. especially in the first year or two, i'd suggest re-testing TSH/T3/T4 every few months until you figure out which dose is right for you. remember that more than anything (time of day, diet, etc) you have to be consistent in when/how you take your drugs.
although i don't have that massive fatigue any more, i'd say i really haven't felt 100% since i first developed thyroid disease. at my best i'm still a 95%, i think. on the other hand, i guess i'm older! what i do get, though, are the emotional side effects - the first symptom that my thyroid's off is if i start feeling cranky, depressed, or short-tempered. if that continues for very long, it's almost a sure sign that i need another blood test.
i'd also suggest to be a little wary of your doctors. not trying to be disrespectful, but i've had several docs tell me "oh, you don't need to test your thyroid more than once every couple of years!" sure enough, they test it and it's out of whack and needs changing. . . again. there's almost zero research on how thyroid's affected by things like triathlon training, and lots of conflicting research on how it's affected by diet and other medications. can't comment on the diabetes connection but i'd be talking to an endocrinologist if you can.
anyway, not to be too depressing. the great news is that thyroxine is cheap, stable, easy to get all over the world, and side-effect free. it's a pain to have to take it for the rest of your life, but a relatively minor one all told and since the alternative is sleeping 20 hours/day, it's practically a miracle cure! this summer won't be your best racing season ever, but in a few months you'll be ready to rock again. in a few years you'll hardly even remember this whole thing.
good luck and keep us posted!
____________________________________ http://utoronto.academia.edu/MikeCallaghan http://howtobeswiss.blogspot.ch/