When your thyroid is functioning normally, the thyroid is part of a feedback loop with your pituitary gland. The way its starts is that the pituitary senses the level of thyroid hormone that the thyroid has released. In turn the pituitary releases a messenger hormone known as the Thyroid Stimulating hormone, or TSH for short. This hormone’s job is to then to stimulate the thyroid to release more thyroid hormone.
If the thyroid is not producing enough hormone the pituitary, in turn, releases more TSH to help trigger the thyroid into producing more hormone. If your TSH is higher than normal, the test suggests you have an under active thyroid. So high TSH means under active thyroid (hypothyroidism).
An overactive thyroid would be producing to much hormone so the pituitary either slows down the TSH production or shuts down completely. So low levels of TSH means overactive thyroid (hyperthyroidism).
Thyroid problems are very common, and do not discriminate against age or sex. It would not be a bad idea to keep the level of your TSH monitored yearly. It can save you a lot of frustration, trust me!