Just because your levels are in the "normal" range, doesn't mean they are adequate. Since you're only taking half the prescribed amount, obviously, it can't be doing what it's meant to do.
It would be helpful if you'd post your actual levels so we can see what they are. Please provide reference ranges, also, as those vary from lab to lab and have to come from your own report for the best comparison.
Thyroid hormones affect every part of your body and not having enough has an adverse effect even though you might not feel it for a while.
We'll be able to comment more fully once we know your actual levels and their reference ranges...
My TSH Reflex turned out to be 3.37 uIU/mL with a reference range of 0.3-5.5.
I cannot find my levels when I was taking 75 micrograms every day.
However, the range seems pretty good to me, I would think.
The range used by your lab is an old one and way too broad... most ranges for TSH only go to about 4.5, but even at that the test for TSH w/reflex is an outdated test and shouldn't even be used anymore. 3.37 is toward the higher end of the range.
You should be tested for Free T4 and Free T3, which are the actual thyroid hormones. TSH is a pituitary hormone and does not correlate well with thyroid hormones, especially when one is on replacement hormones. Most thyroid doctors who do look at TSH prefer to have it <= 1. Because your doctor is ordering an outdated test, I'd say s/he is not well versed in thyroid testing/treatment.
Of course, we can't tell you what to do; the choice is yours but medication changes should always be discussed with your doctor.