When you get your bloods done get your T3 & T4 done as well as your TSH.
Each area has it's own "levels" for what is "normal" - and this just depends on where the bloods are analysed but as a rough examplemore info here. www.endocrineweb.com/thyroid-what-are-t3-t4-tsh When you get your blood results the ranges are normally indicated in the results list too.
Many GPs just look at the TSH level as a guide for if you are on the right medication. Or will just see that your T3/T4 are within normal. However the "normal range" can be quite large and if you are mid-range yes, you "tick the box" as far as the numbers are concerned. The results will say "no action required". The GP receptionist will say "they are normal" and you will be filed as "done". But this does not mean you are at the right level for you - but it means you will need to follow it up if you think you need to. I would recommend it is worth a thought if you results are "mid-range-normal".
Over the years I have been able to tell when my levels are too low. Peri menopause has had an affect, ageing, diet.
Symptoms wise I begin to get a few of the old niggles back (heavy periods, tireness, coldness, slightly constipated and yes, weight gain when nothing else has changed). Nowhere near as bad as pre-medication - but just hinting towards it.
As an example my T4 (I think it is T4) range is in our area 16-21 ish where my bloods are done. When these symptoms start to come back...no suprises, my bloods are within "normal" but are about 17/18. If however I increase my dose, even just slightly (I take 100 on 5 days a week and 125 on 2 days a week) then they symptoms disappear and my bloods are at 19/20. And I feel great. And my weight is maintainable (and/or I can lose weight with normal calorie controlling/diet rather than extreme).
If I increase too much (and so bloods are at eg the 21 level - then actually, I start to feel a bit anxious/jittery and unpleasant. Too much.
So, sorry - long story - really check your levels. And if you are mid-range with your results say to your GP, "I really am having some symptoms again, please could we do a 3 month trial of an increase to see if the symptoms disappear" and suggest a small increase. And if they protest ask what would make them happy to allow it? Especially as the the NICE guidelines say. Reiterate patient choice. Ask what are the risks? NICE does say:
Aim to maintain TSH levels within the reference range when treating primary hypothyroidism with levothyroxine. If symptoms persist, consider adjusting the dose of levothyroxine further to achieve optimal wellbeing, but avoid using doses that cause TSH suppression or thyrotoxicosis.
and
Even when thyroid function tests are within the reference range, changes to treatment may improve symptoms for some people.
Whole guidelines here: www.nice.org.uk/guidance/ng145/chapter/recommendations
You cannot use too much Levo as a weight loss treatment - not good for heart, too much feels awful, awful, awful, but too low a dose really can mean weight gain and/or make it nearly impossible to lose weight. In addition, if you gain weight, you potentially need more Levo (your weight is how the starter dose is calculated) .