hi Abigail. there are still too many doctors who don't believe in medical conditions they can't see or don't show up in test results.
it could be a case of ME and fibromyalgia although they can mimic more serious conditions. you really need to see a different GP at the surgery or change surgery all together.
even without a diagnosis there is strong pain relief available, residential ME/CFS and fibro courses to learn how to live with the conditions, referrals to a rheumatologist, a neurologist and a pain specialist, disability benefits/blue badge/disabled bus pass, social services help for aids and adaptations such as a hospital style bed, a stairlift, instillation of a wetroom, grab rails, a wheelchair etc, eligibility for a housing association bungalow.
whatever is wrong with you, you are disabled and have rights. ESA and DLA benefits pay over £1000 a month for the most disabled people. DLA pays well so you can get a cleaner, a carer, taxis etc but it also opens doors to many discounts such as discretionary 2 for 1 entry to events so you can take a carer and a CEA card to get 2 for 1 at the cinema. higher rate mobility component of DLA gives you free car tax.
it's not all about money but with the money you can get the help you need, a social life as you're so young, and the chance to go to uni if you want to as they give out more money for equipment you need to help you. also if you want to leave home, if you get the middle rate care component of DLA you can get housing benefit on a 1 bed place not just 1 room. maybe even save up to see a specialist(?)
best wishes sweetheart, i know how you feel, A x