Upper back aches, constant fatigue, always cold, tingling in right knee, constant headache? Borderline thyroid issues. Could it be hypothyroidism?

Possibly. Hypothyroidism is a possibility and is easily diagnosed by elevation of the TSH level. Other possibilities include anemia,low iron levels,low blood pressure, slow heart rate,vitamin deficiencies,chronic anxiety. Your physician who has examined you knows best what tests to order to complete your evaluation.