The relationship between thyroid hormone status and menstrual periods can be complex. In general, when a woman of reproductive age (and not on birth control pills) has 'hypothyroidism' ie an underactive thyroid, she would typically experience heavy periods. On the other hand, in hyperthyroidism ie an overactive thyroid, one can expect shorter cycles with light flow. However this is not rigid and various menstrual disturbances are possible.
The best way to approach this is to have a blood test to check for current thyroid hormone levels like a TSH, free T4, Total T4, Total T3 and T3 resin uptake along with a CBC, CMP and possibly FSH, LH, prolactin, Thyroid peroxidase and Thyroglobulin auto antibodies. If these are not abnormal then the thyroid is unlikely to be responsible for your menstrual irregularity.
Regardless it is best to consult a gynecologist for issues pertaining to menses. There can be several other potential reasons for absence of your cycles and merit a thorough evaluation

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