Order TSH (thyroxine-stimulating hormone) blood testing online
In the majority of US states you can order TSH testing online and have the blood drawn at a local blood draw center (see my general overview of the process).
I'd suggest ordering from Life Extension because they have the cheapest price I know of ($31), and I've been happy with their service. You can also compare the other 6 TSH test providers I've found.
Take a look at my state-specific issues page if you're in AZ, MD, NJ, NY or RI.
Understanding the results
I think my (slightly-silly) video gives a good overview of TSH that helps you avoid misinterpreting it:
The American Association for Clinical Chemistry has helpful pages for understanding the test and answering common questions.