Well…several things come to mind!
First when were you diagnosed with hypothyroidism and have you altered your nutrition and exercise patterns significantly since then? It might be a good idea to get that checked again.
Second thing, when you say: “dieting is somewhat difficult” I’m guessing you have had problems getting to a level of leanness you want? Me being the curious type…what does your nutrition look like? Are you getting several (4-5) meals per day with 3-6oz of protein like chicken, fish or beef at every meal? Plenty of veggies? No wheat, and a minimum of other grains and dairy (if your hypothyroidism is an autoimmune situation this recommendation of cutting the grains, soy and dairy could be VERY important). If these things are not in place it will be very hard to carry a low body-fat level and hey, it’s not dieting it’s just “good eat’n” :0)
Ok, third thing: bio-identical hormone replacement (BIHR) can be appropriate for both genders. That said I am assuming you are female, if I’m wrong please recommend any punitive retribution that seems appropriate! Try to find a doctor who specializes in BIHR. These doctors are hard to find but they exist. The book “Sex, Lies and Menopause” is also a must read (discusses BIHR).
Fourth thing and actually getting back to your original question! If you are not getting adequate iodine adding 1/8th tsp of powdered kelp per day for a few weeks might be helpful. Another product called guggul lipid can help in the conversion of T4-T3. But as this link points out it may be a conversion issue and or a lack of thyroid stimulating hormone (TSH): http://www.altsupportthyroid.org/t3/t3medrefs2.php
It is NOT at all a clear-cut situation and a good doctor who actually remembers their endocrinology and has a good diagnostic lab can help you ferret out what is really going on. People try the self-diagnosis thing and do OK but if you can get some help in this area it can be quite beneficial. We work with an amazing doctor here in Chico, CA Dr. Nagel. Great doctor, fantastic person. He may be a resource for finding a good Doc in your area.
Just to re-cap: You can do a lot of stuff revolving around nutrition and exercise that will help regardless of your hormonal status. Get those dialed and if you need help doing that just let us know. If that is not getting you where you want to go think about finding a doctor that can help. Remember a good doctor can help, a bad one…well, yeah anyway…just find a good one! If you embark upon any of the supplements that are available it would be wise to know what your T4/T3 levels and TSH are so you can know that things are actually in need of help or that your intervention is doing something.
Sorry for the long response! Let me know if this helps.