Welcome to the forum, Vm133.
TSH is a pituitary hormone. TSH responds to thyroid hormone levels (T4 and T3). When the pituitary gland detects low T4 and T3 additional TSH is produced to stimulate more thyroid hormone so TSH rises. When sufficient T4 and T3 is detected TSH drops.
Thyroid is a sort of master gland affecting many organs. Hypothyroidism can reduce function of liver, kidneys and heart which is why your GP is checking kidney and liver function and FBC. This link explains what a FBC is labtestsonline.org/understa... Cholesterol is often high in undiagnosed and under medicated thyroid patients. It should come down when you are optimally medicated on Levothyroxine.
Ask your GP to check ferritin, B12 and folate as these are often low/deficient in hypothyroid patients. Post the results and ranges (figures in brackets after results) in a new question for advice on whether to supplement. You could also ask your GP to test thyroid peroxidase antibodies to see whether your hypothyroidism is autoimmune.
What is your vitaming D result?
After every blood test ask your GP or GP receptionist for a copy of your results with the lab ref ranges.
Now you are having low thyroid hormone replaced with Levothyroxine you may find that weight gain slows down. You may need to restrict calories and exercise to lose the weight already gained but you should delay doing either until you are optimally medicated.
For maximum absorption Levothyroxine should be taken with water 1 hour before or 2 hours after food and drink, 2 hours away from other medication and supplements, and 4 hours away from calcium, iron, vitamin D supplements and oestrogen.
It takes 7-10 days for Levothyroxine to be absorbed before it starts working and it will take up to six weeks to feel the full impact of the dose.
You should have a follow up thyroid test 6-8 weeks after starting Levothyroxine. Arrange an early morning and fasting (water only) blood draw when TSH is highest, and take Levothyroxine after your blood draw.
Most people will find symptoms resolve after their TSH drops to around 1.0 with FT4 in the upper range but symptoms can lag a couple of months behind good biochemistry.
I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.