What to expect - in all likelihood expect to have GPs that don't understand the condition properly, don't treat it properly, and insist that if your numbers are "in range" then you are fine.
Get yourself over to the Thyroid UK website as they have lots of useful information, and also the Health Unlocked forum (thyroid section) from there. I have learnt so much from there in the last year.
I also went to the Drs with mega heavy periods, and ended up getting a private blood test done through Medichecks ironically to rule out thyroid issues (Dr was being less that helpful). It turns out I actually have hashimoto's.
Despite being medicated now (which I had to fight for and be assertive to get it raised every 8 weeks after blood tests) and supposedly having really good blood test results (I make sure I get copies of all my tests) I feel dreadful. I'm exhausted, have brain fog, have put on tonnes of weight which i just can't shift even if I try and diet, hairloss, pain all over my body and all kinds of other symptoms. My ferritin levels are low, but because they are "in range" the Dr won't do anything about them. Hairloss can occur if your ferritin is below 50, which mine is, but all they care about is the numbers.
I've gone gluten free, worked hard on trying to get all my vitamin levels up (very important) and still feel like crap. I managed to persuade the Dr to refer me to an endocrinologist, but because of COVID nowhere is currently dealing with new referrals.
My health has gone downhill dramatically in the last 18 months are so. I currently use a walking stick when out and have just ordered a wheelchair. From all the research I've done I seriously believe that all my issues stem from my thyroid.
Sorry to be so negative. When I got my blood tests back indicating thyroid disease I really had no idea just how bad things could be, and how badly it is dealt with. The health unlocked forum is a real eye opener, and there are some very well informed people on there who have definitely helped me way more than the GP.