First thing is do you have any actual blood test results? If not you need to get hold of them. You are entitled under data protection laws.
You may be able to view test results online - ring and ask about this. If you can then apply for online access to your account. All GP practices are supposed to offer this, in reality very few have blood test results available online.
If not then ask for print out of recent tests. Pick up in a day or two. They may make a nominal charge for paper.
You need to know results for TSH, FT4 and FT3.
Do you also have high thyroid antibodies? You need to know. Did GP or Endo ever test these? If not ask that they are tested.
If antibodies are high this is Hashimoto's, (also known as autoimmune thyroid disease). About 90% of hypothyroidism in UK is due to Hashimoto's.
Hashimoto's very often affects the gut, leading to low stomach acid, low vitamin levels and leaky gut.
Low vitamins that affect thyroid are vitamin D, folate, ferritin and B12. If they are too low they stop Thyroid hormones working. Have these been tested, if not ask that they are.
Always get actual results and ranges on all blood tests
If you can't get full thyroid and vitamin testing from GP
Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers. DIY finger prick test or option to pay extra for private blood draw or
All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH and most consistent results