Thyroid being a mix of high/low symptoms.... Hashimoto's?
Everything you write is screaming "multiple autoimmune conditions" IMO. Including the family history (your brother).
Sadly, in this area of medicine, knowledge is lacking/only just emerging (the autoimmune cause/contribution of many diseases is only recently understood).
You have had Coeliac testing, so either you don't have it, or have "false negative", which is surprisingly common.
Negative or not, you have a long list of symptoms consistent with ceoliac or a serious non ceoliac reaction to gluten and/or other grain proteins.
IMHO you should try to seize control and try an exclusion diet COMPLETELY free of all grains, google "whole30", "Marks Daily Apple", "Robb Wolf The Paleo Solution". You will find a wealth of information (and so many success stories of people regaining health by cutting out wheat and other grains). There are immune protocol exclusions (all the info you need to do this safely). In a month, (or as in my case, a few days!), you will have an answer- either grains are making you ill (not necessarily the gluten, could be other thing in the grains), or it's not... You have nothing to lose by giving it a wee try for a month. Word of warning tho' - you may initially feel quite unwell (flu like), for maybe 3 or 4 days. This is literally withdrawal symptoms.
If you feel no better grain free (I'd be very surprised!), then at least you know for sure that gluten/wheat and other grains are not making you unwell... And surely that's valuable information too
!?