Hi Claire:
I started having thyroid issues ~4 months into breastfeeding (Jan 2009) and ended up severely hypo after a short episode of being severely hyper for about 5 weeks.
I too was immediately put on Synthroid without much explanation/discussion. (FYI: When I went to have the Rx filled they gave me levothyroxine at first, and then they refilled my script with levothroid just a few months ago b/c they were out of levothyroxine -- both are generics for Synthroid but its really important to just stick with whichever one you start on as the hormone levels are slightly different and the change made all my hair fallout a second time!!)
I was freaked out and really wanted to stay as natural as possible, so I sought out some known successful alternate therapies in addition to agreeing to take the drugs after being reassured thru tons of research and a lot of pointed questions to 3 different drs that it was 100% safe for the baby. I did acupuncture and chinese herbal medicine (this was hard b/c no research on impacts of breastfeeding and some of the time the herbs had crazy impacts on the baby's poop color, etc) but I do feel it helped me get out of the hole I was in energy level-wise so I could start functioning more at my old-self, pre-kid level.
I stopped the chinese herbs and I have not been able to go off the drugs yet, because I got pregnant with our second right after my son's first birthday this fall. (happy accident!) I did start to feel like things might be self-correcting at that time -- as they do for about 80% of women around 12-18 months post-natally -- and was excited I might be able to try weaning off the drugs. (My dr was not as enthusiastic about this, but was going to support me)
Needless to say, I was pretty bummed when I was referred to an Endo to watch my thyroid thru the second pregnancy -- since your metabolic needs change each trimester and everyone felt a specialist was in order. She basically said while my levels all looked good (and I successfully got pregnant) that we shouldn't rock the apple cart and think about going off the drugs or switch to Armour (a natural version of the thyroid hormone taken from pigs) until I weather the storm of my second post-natal go round.
Given everything I have read (and its a lot, I even bought Dr. Langer's thyroid book "Solved") and everyone I talked to, I have thru the course of the year decided it is not that big of a deal to take the drugs. They really do help. (I do also recommend acupuncture but its harder to find the time and money to be consistent at it.)
If its any consolation, your dose is super tiny. But expect that they may have to ramp it up a little after your next round of tests. Also, I prefer to get the whole panel not just T4, but that's b/c I am a control freak. It really doesn't change anything in terms of your treatment plan.
Not sure if that helps, but feel free to ping me if you have more Qs.
-J.
p.s. If you are breastfeeding and/or still taking a prenatal vitamin you should not (according to what I have read) take kelp/iodine or any other mineral supplements like zinc, etc. Supposely evening primrose oil helps with the hair falling out but I can't find anything about if its safe for breastfeeding or pregnancy. But Omega3s for memory, etc are ok.