I know, times before my tests showed, "within normal limits" but I was having every symptom, and yet they refused to give me Synthroid, the joke is in a couple of months, tests showed I needed supplementation.
So many books, and internet websites say what I feel, if a person, as an individual is having the symptoms, what wrong is it to try meds. rather than sending them for all tests, I'd rather try one thing, then go on to another if no results occur. I had already lost so much hair, focus, etc.
that I think if my doc would have just realized "within normal range", for thyroid, is not always normal for everyone, I hope they update the thyroid function blood tests done at the lab(s).
My present doc, did request TSH levels, stating this tests gives a more exact idea to what is happening, too high of levels TSH (thyroid stimulating hormone) indicates hypothyroidism (sluggish thyroid function) which is common in middle aged women as well as the young.
If tests indicate low levels of TSH, hyperthyroidism can be the culprit, weight loss, or unable to gain weight (wish that was my case, ha!ha!) besides a lot of other symptoms, hyp and hyper thyroidism both have quite a lot of symptoms, but I won't start listing them, cause I am sure all that you have been going through, they must of given you some of those free pamphlets at the doc's office, that explain or at least list the symptoms.
I wish you lots of luck with this, I know how frustrating this gets.
One of the books I bought about thyroid disease, comes from the UK, the title is "Thyroid Disease the facts", I found this an informative book. The authors names are:
R.L.S. Bayliss and W.M.G. Tunbridge
Published by : Oxford University Press
If you can find this where you live, the info might help, and may help your doc understand more.
Can't hurt, give it a try.
Again, I wish you lots of luck, and let us know of the outcome.

Take care,
DE