The thyroid and adrenals are a codependent system. You can not treat one and ignore the other if you have an issue with BOTH. You are saying you have low adrenal results. Please expand on this. Do you have low aldosterone, cortisol, ACTH? Level and ranges? I need specifics to give any educated replies. Normal thyroid results are not always optimal and definitely may not be balanced. What are your TSH, Ft3, Ft4 levels and ranges?
NOW ASSUMING YOU MEAN LOW CORTISOL:
1) You have to look at your B12, Ferritin, vit D levels. You want them to be at least 50% of normal range.
2) You need to supplement your low cortisol with hydrocortisone tablets.. standard dose for adrenals not producing cortisol is 20 mg - 4(5 mg) tablets.
3) You have to learn when you need to take your HC tablet and stick to the regime.
4) It can take 3 months for your adrenal response to stabilize on a regimented HC supplement scheme.
5) When your cortisol output is regulated and optimal for you, your Ft3 and Ft4 levels should be with in 10% of each other.. barring conversion error due to excess RT3 production.. but that is a different organ T4 processing issue.
IF you are SUBOPTIMAL in thyroid levels. BELOW the 50-80% normal range in Ft4 and Ft3.. supplementation of the thyroid could help you. If your cortisol levels are too low, you run the risk of driving yourself hyperT in T3.. T3 toxicosis. So you have to go slow on the thyroid supplementation until the adrenal issues are regulated.
You may need to just start on 25/50 mcgs T4. And hold while your adrenals adjust. You can not treat one with out the other. You can not NOT treat the adrenals and hope treating your thyroid will solve the issue. To do so will almost guarantee you a visit to hyperthyroid land.
Now have you been tested for Hashimoto's thyroiditis?
Have you been tested for Graves?
Have you had a thyroid ultrasound? Any nodules?
Have you had an iodine uptake scan?
Your transient thyroid issues and adrenal issues really smacks of untreated and poorly managed Hashimoto's. But with out having the tests you can not rule it out. Hashimoto's is a difficult beast to treat, BECAUSE when your immune system is killing off thyroid tissue you get sporadic T4 hormone dumps in your system. Early in Hashimoto's this can cause hyperT swings that are not detectable by TSH testing alone. Hashimoto's can hit you hard even before your FT levels fall below low normal range. ALL because the thyroid CAN NOT chill or calm down. It is hard to CALM down when you are under constant siege. Now if you get a copy of your lab results and post them I will be able to Ohhh, Ahhh.. and speculate in a more personal manner.