Here are some things to pursue in getting a diagnosis.
What is your lab's "normal" range, and how does your doctor define "normal?"
Different labs have different values for what is normal. For example, at the lab my doctor uses, the normal range is .5 to 5.5. A TSH of less than .5 is considered hyPERthyroid, and a TSH of more than 5.5 is considered hyPOthyroid. Other labs might use .35 to 5, or .6 to 5.2, etc., but it's important for you to know the values at YOUR lab.
AND, it's important to know that as of March, 2003, the endocrinology community has recognized that the normal range is actually narrower. While labs are not necessarily reflecting this in their testing, the official "normal range" is now .3 to 3.0. For more information, read: Endos Say Normal TSH Range Now .3 to 3: Millions More at Thyroid Risk.
If you're on the higher end of the normal range, you could very well be borderline hypothyroid for YOU, but still in the "normal" range. So, you need to know what TSH level your doctor is targeting for you. This is a very loaded, but VERY important question. Your doctor's answer will tell you her or his philosophy about "normal" TSH. Some doctors believe that being in, or getting you into the very top of the normal range is their sole objective, and then the job is done. So, for example, using the 5.5 outer edge of the TSH level from my lab, that sort of doctor believes that getting me to somewhere around there constitutes full treatment.
Other doctors believe that certain TSH levels within the normal range are more appropriate targets. My endocrinologist, for example, believes that women don't feel well (and can't lose weight or get rid of other hypothyroidism symptoms) unless TSH is down between 1 and 2, far below the higher end of "normal." (There are some suggestions in research that have shown that the average TSH of a women without thyroid disease is 2, so that may be why some women don't feel well at 4 or 5.) My doctor wants me to feel as well as possible within normal range, but finds that on average, women don't feel well at the higher end, so she aims to take it lower.
In my own experience, I feel downright awful at anything above 4, and I feel great between 1 and 2, which is where my endocrinologist keeps my TSH. But some doctors would have no problem keeping me between a TSH of 3 and 4, still in the laboratory "normal" range, despite the fact that I still have the full range of hypothyroid symptoms -- fatigue, weight gain, irregular menstrual periods, dry skin, hair falling out -- at those levels.
The best doctor is one who believes that managing your thyroid is a combination of TSH AND how you feel. These are doctors who treat you like a patient, not a lab value! These doctors might say "well, let's get you into the normal range, see how you feel, and adjust the dosage from there."
Have you been tested for thyroid antibodies?
Some doctors believe that a thyroid that is in the process of autoimmune failure -- as evidenced by elevated antibody levels -- can cause hypothyroid symptoms BEFORE the hypothyroidism shows up as TSH outside the normal range, and should be treated with small doses of thyroid hormone.
One doctor who lays out this information is Elizabeth Lee Vliet, M.D., in her book Screaming to be Heard: Hormonal Connections Women Suspect...and Doctors Ignore. Dr. Vliet does not believe that TSH tests are the almighty indicator of a woman's thyroid health. Dr. Vliet says that symptoms, along with elevated thyroid antibodies and normal TSH, may be a reason for treatment with thyroid hormone. Here's a quote from Dr. Vliet:
The problem I have found is that too often women are told their thyroid is normal without having the complete thyroid tests done. Of course, what most people, and many physicians, don't realize is that...a 'normal range' on a laboratory report is just that: a range. A given person may require higher or lower levels to feel well and to function optimally. I think we must look at the lab results along with the clinical picture described by the patient...I have a series of more than a hundred patients, all but twoare women, who had a normalTSH and turned out to have significantly elevated thyroid antibodiesthat meant they needed thyroid medication in order to feel normal. This type of oversight is particularly common with a type of thyroid disease called thyroiditis, which is about 25 times more common in females than males...a woman may experience the symptoms of disease months to years before TSH goes up..."