Thats not true you can have a deficiency in just one hormone. And if your tsh is low and so is your free t4 (at bottom of range) you could have a pituitary issue. Please post your results so we can comment accordingly.
High and low thyroid levels, in my experience are not indicative of a pituitary tumor. The pituitary controls all your hormones. Sexual(Testosterone or estrogen) , adrenal, HGH, and thyroid. If you have a pituitary tumor all of your hormone level, in my opinion would be off.
Good pituitary tests are: prolactin, FSH, alderosterone, GH, cortisol, also lipid panel, cbc and comp should be done... in addition to thyroid and possible even glucose tolerance. Pituitary affects a wide variety of endocrine functions.
I hope you get this, your thyroid levels can be fine they need to check for free T4, LSH and fsh and most of all a prolactin level where most pit tumors are prolactin secreting. Learned from experience good luck
My docs like my thyroids like this - TSH in the low end (when I had a normal TSH to look at, forget that now) and the rest in the higher ends of the ranges - that is how I felt best.
As for can you have an issue with a normal thyroid - yes. I had Cushing's disease with a TSH that was in a normal range. However, my TSH would bounce all over the place, making my thyroid impossible to regulate.
Can you get your GP to run a 24 hour cortisol test?
Hey the normal ranges are just ranges. Many of us seem to feel better when our levels are at the higher end of the range. Everyone is different. I don't see why your doc might not try you on a low dose of thyroid medication to see if it helps you to feel better. You might present it that way? Just say that you would like to try it and back it up with any symptoms that you think are due to your thyroid levels being a the lower part of the range. IE dry skin, hair falling out, low body temp, cold intolerance, constipation, weight gain etc. The possible symptoms are a long long list. And it is amazing what one little pill can do if your levels are lower than they should be for you.
It may or may not be pituitary related. But a full panel of pituitary labs done to rule that in or out. Some of us pit patients make TSH (the hormone that that pituitary gland makes to stimulate the thyroid to do it's job) but we are low in growth hormone or other things.
Hope this helps.