As you mentioned, I agree, your medications may be a factor for the tiredness and weak. Apart from thyroid diseases and iron issues (which you have may be the concomitant factors), the other causes to look for would be;
1) Chronic fatigue syndrome; though not common in your age group and also is less common in males.
2) Connective tissue disorders
3) Anxiety and depression
4) Addison's disease
5) Chronic anemia
6) Chronic infections
7) Liver or kidney disease
Following may be recommended, if not yet done:
1) Complete blood count,
2) Erythrocyte sedimentation rate,
3) Comprehensive metabolic panel
4) Muscle enzymes;
5) Anti-nuclear antibodies (ANA)
6) Adrenal function test
9) Anti-SSA (Ro) or Anti-SSB (La)
10) Coombs test
People who have episodes of fatigue or tiredness (or persistent symptoms) need to be classified in;
1) chronic fatigue syndrome; unexplained, persistent or relapsing fatigue with unrefreshing sleep, muscle pain, concentration problems, headache, sore throat etc.
2) idiopathic fatigue; it does not meet the above criteria.
Fibromyalgia, lupus, sleep disorders are the other disorders which should be looked for your symptoms. Other investigations necessary are (many of which have already been done):
1) Complete blood count (CBC)
2) Peripheral blood film
3) Vitamin B-12
5) Reticulocyte count
7) Thyroid-stimulating hormone
8) Serum creatinine and estimated glomerular filtration rate
9) Serum ferritin
10) Serum iron
11) Total iron-binding capacity
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
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