I am Hypo due to Hashimoto's and have lower back pain and fatigue also, and I understand it is not uncommon among Underactive thyroid, so I assume you are on Thyroid Hormone replacement medication, you might need an increase in your medication.
Have you had a Free T3 and Free T4 tests done recently? If so post your results with the reference ranges provided for each and TSH also. If not, then maybe you should have these tests done. Good Luck FTB4
Thyroid tests when "normal" can definately be challenged by the patient however, did they run any other tests also like a vit B or D test. That could also contribute to fatigue.
Having gone without medication for hypothyroidism for years and then being improperly medicated for an even longer time, I know how frustrating it can be. This is especially true when the doctor is telling you that all your thyroid tests are "normal" and that nothing further is needed for thyroid. When you are still having hypo symptoms, that is just WRONG!
Many doctors have the "Immaculate TSH Belief" and only want to diagnose and medicate you based on TSH. TSH is a pituitary hormone that is affected by so many variables that it is inadequate as a primary diagnostic. At best TSH is an indicator to be considered along with more important indicators such as symptoms and also Free T3 and Free T4. Free T3 is the most important thyroid hormone test because it largely regulates metabolism and many other body functions. Scientific studies have shown that FT3 correlated best with hypo symptoms, while TSH and FT4 correlated very poorly.
So it is very important to be tested for the biologically active thyroid hormones, Free T3 and Free T4. Even if a doctor agrees to test for FT3 and FT4, frequently they use "reference range endocrinology" and declare that any test result that falls within the reference range, even if in the very low end, is "normal" and nothing further is required. Actually this is very far from reality. The reference ranges are far too broad. The reference ranges should be used as guidelines within which to adjust FT3 and FT4 as necessary to relieve symptoms. Symptom relief should be all important, not test results. Many members report that symptom relief for them required that FT3 was adjusted into the upper part of its range and FT4 adjusted to at least midpoint of its range.
So if not done previously, it is very important that you get tested for Free T3 and Free T4, along with TSH. The most important thing for you to do is to make sure you have a good thyroid doctor. By this I mean a doctor that is wiling to treat you clinically by testing and adjusting FT3 and FT4 as necessary to relieve symptoms, without being constrained by resultant TSH levels. Remember that symptom relief must be all important, not test results. By the way if you look through this list of typical hypo symptoms, I expect that you will find that you recognize more than just fatigue.
http://endocrine-system.emedtv.com/hypothyroidism/hypothyroidism-symptoms-and-signs.html
You can get some good insight into clinical treatment by reading this link. It is a letter written by a good thyroid doctor for patients that he is consulting with from a distance. The letter is sent to the PCP of the patient to help guide treatment.
http://hormonerestoration.com/files/ThyroidPMD.pdf
There are a number of very experienced and knowledgeable members here who are very willing to help. So please post your FT3 and FT4 and TSH test results, and reference ranges shown on the lab report, when available, and members will be glad to help interpret and advise further.