Just to reinforce that...

Some specialists have come to believe that the current range considered 'normal' is not a sufficient measurement of thyroid function. Many of the normal ranges are determined statistically (i.e. if a certain percent of the population is considered normal, then that's what's considered normal. But that's like determining 'normal' weight based on average weights in a society which may have high rates of obesity. Your weight may be right smack in the middle of average, but that doesn't mean you're at a healthy weight. Same with thyroid. But most doctors don't realize that.

The other thing is that even if you are in a healthy range overall, doesn't mean you are at a level that's optimal for you. Just because someone's weight is in the healthy BMI range doesn't mean that the person is at a healthy weight. Someone who is very fine boned and has very little lean muscle mass and whose natural BMI is 20, would be just as unhealthy at 25 as someone who is large-boned might be at a BMI of 30. Similarly, someone who is large boned may not be healthy at a BMI of 20, even though it's technically classified as healthy.

My point is that the numbers aren't always as meaningful as we (and doctors) think they are.

What makes things even more difficult is that the standard thyroid tests don't actually measure the level of thyroid hormone in your body - they measure the hormone that tells your body to produce more thyroid hormone. So you may have low thyroid hormone, but your body doesn't detect that, so it tells tells your endocrine system not to produce any more thyroid hormone. This kind of problem is becoming more common partly because we have so many chemicals in our food etc that disrupt the endocrine system. I recently switched toothpaste when I found out that the brand I was using (Colgate) is the only major toothpaste brand that contains triclosan, an antibacterial agent that disrupts the endocrine system, especially the thyroid signalling system (best to avoid triclosan altogether, not just in toothpaste - if you want to use a hand sanitizer make sure it's alcohol based.)

Another thing that could go wrong is that your body may detect the insufficiency, but not be able to produce the hormone that tells your body to produce thyroid hormones, so your tests would come out normal. There are also some people who actually do have normal thyroid hormone levels, but their bodies are not able to use that properly. So there are several conditions that can result in normal tests but still have symptoms of low thryoid function.

For years I had symptoms of low thyroid function but always tested in the normal range. Finally, I had one doctor who suggested trying a low dose thyroid hormone (I take cytomel) and it helped alleviate my symptoms.

My current doctor once told me that there are a lot of people who have symptoms but test normal, and they refer to it as subclinical hypothyroidism. She also said that back when they didn't have lab tests, they went entirely by symptoms, and it seemed to be more accurate. Funny that. So even though you may appear to have your thyroid hormone levels at an adequate level, they may not be.

I don;t know what your diet and exercise program is like, but if you do have any other symptoms of low thyroid despite your 'normal' tests, it's very likely that your dose isn't adequate for you.