High TSH but FT4 and FT3 normal

That is peroxidase antibodies? Yes, they are an issue, they mean you have Hashimoto's Thyroiditis.

There problem here is that 'in range' is meaningless. And just 'in range', is not good enough. Your FT4 is right at the bottom of the range, and your FT3 is under mid-range. That's just too low for your to be well, and that's why the TSH is high.

The TSH doesn't know what the ranges are. They were made arbitarily by someone in a white coat, and they are not optimal for everyone all the way through - how could they be? The TSH just knows that there is not enough hormone in your blood, and so it increases (well, that is to say, the pituitary knows there's not enough thyroid hormone in the blood, so produces more TSH to stimulate the thyroid gland to make more hormone, only yours cannot make more because it has been damaged by the antibodies.)

You need to find your own sweet-spot, of course, but I very much doubt that is would be right at the bottom of the range for anyone. Have a look at what Diogenes says about ranges in this thread :

healthunlocked.com/thyroidu...

So, as you appear to be converting your levo into T3 very well, what you need is an increase in levo. And, when your T3 rises, you will find it easier to lose weight.

Suggest you ask GP to check levels of vitamin d, b12, folate and ferratin. These all need to at good (not just average) levels for thyroid hormones (our own or replacement ones) to work in our cells. Common with Hashimoto's to be be low in some, or all of these. Hashi is often connected to leaky gut - causes low nutrients

As you have Hashimoto's then you may find adopting 100% gluten free diet can help reduce symptoms, and lower antibodies too. Selenium supplements can help too

Assume you know that Levo generally should be taken on empty stomach and no food or drink for at least hour after.

Many of us take on waking, some prefer bedtime, either as more convenient or perhaps more effective.

verywell.com/should-i-take-...

No other medications at same time, especially iron or magnesium, these must be at least 4 hours away

Vitamin and minerals levels are very important, but standard NHS thinking, doesn't at the moment seem to recognise this. You will see, time and time again on here lots of information and advice about importance of good levels of B12, folate, ferritin and vitamin D, leaky gut and gluten connection to autoimmune Hashimoto's too.

If you can not get GP to do these tests, then like many of us, you can get them done privately

thyroiduk.org.uk/tuk/testin...

Blue Horizon - Thyroid plus eleven tests all these.

This is an easy to do fingerprick test you do at home, post back and they email results to you couple of days later.

Usual advice on ALL thyroid tests, (home one or on NHS) is to do early in morning, ideally before 9am. No food or drink beforehand (other than water) If you are taking Levo, then don't take it in 24 hours before (take straight after). This way your tests are always consistent, and it will show highest TSH, and as this is mainly all the medics decide dose on, best idea is to keep result as high as possible

drgominak.com/vitamin-d-hor...

vitamindcouncil.org/tag/aut...

chriskresser.com/the-gluten...