Brief Answer:
Thyroid

Detailed Answer:
Sorry to learn about your bothersome symptoms.

Whether or not an increase in dose from 25 to 50 is justified is completely dependent on the laboratory results of thyroid tests like TSH and Free T4, in addition to findings on physical examination.
When I see someone like you in my practice, I typically order the following blood tests in addition to a detailed physical examination:

CBC (Complete Blood Count, also known as Hemogram; includes Hemoglobin, WBC and Platelet counts)
Electrolytes (Sodium and Potassium in particular)
HbA1c (Glycosylated Hemoglobin = your last 3 months' glucose average). Also known by other names such as GlycoHemoglobin or Glycated Hemoglobin or A1c
Liver function tests (SGOT , SGPT, Albumin, Bilirubin, Alkaline Phosphatase)
Kidney function tests (BUN, Creatinine)
TSH (checks your thyroid)
Free T4 (this too checks your thyroid) Thyroid autoantibodies : Anti Thyroid Peroxidase (TPO) antibodies and Anti Thyroglobulin antibodies
25 hydroxy Vitamin D levels (ideal range 40 to 60 ng/ml = 100 to 150 nmol/liter)

None of these tests require any fasting and can be done at any time of the day Correct diagnosis and treatment requires the opportunity to examine the patient so you must see an endocrinologist in-person.

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