What are your actual thyroid hormone levels? It sounds as though your dosage of levothyroxine might not be adequate or possibly you aren't converting the T4 (Levothyroxine) to the usable T3 hormone.
If you'll post your actual lab results, we'll be able to better help you. Be sure to include reference ranges with any results you post, since ranges vary from lab to lab and have to come from your own report(s).
Many people with hypothyroidism also have certain vitamin/mineral deficiencies which can cause severe fatigue as well. The main one that comes to mind is Vitamin B-12 deficiency; if you've been tested for Vitamin B-12, please post that result with reference range as well. Others include ferritin and vitamin D.
All of these are also necessary for proper metabolism of thyroid hormones so if you're deficient in any one, you may not be getting the most from your Levothyroxine.