First thing to do is get a print-out of your latest blood test results. I am assuming he is prescribing 'water tablets' as you appear 'bloated' (swelling - (clinical symptom).
The first lesson is that few doctors know about clinical symptoms - over 300. Second lesson is never accept 'normal', 'fine', 'o.k.' with regard to the results if you have clinical symptoms, i.e. unexplained weight gain, higher cholesterol, fatigue, etc. Particularly if it runs in families.
We have to educate ourselves if we want to get a proper diagnosis, and recover our health as doctors in the UK appear very unknowledgeable about anything with regard to thyroid hormones dysfunction i.e. only look at the TSH and pronounce the diagnosis. They are ignorant about clinical symptoms as well as ignoring them.
Ask for a print-out of your latest results with the ranges for comments and always request a print-out for your own records.
Blood tests for thyroid hormones should be the very earliest, don't eat before it but you can drink water. If on hormone replacements you allow about 24 hours between the last dose and the blood test and take it afterwards.