how to talk to doctors

ive had unexplained list of symptoms for so long, ive complained to doctors and been referred to specialists and everyrhing but i havent been told theres a single thing wrong wtih me, not after alot of testing (i really sontk no what all ive had done as most of it was seceral years ago) and had most of my problems dismissed as anxiety or depession or normal or something ive been having alot of trouble recently; my symptoms have gotten significantly worse? i have constant fatiue and get flu-like symptoms after doing LITERALLY ANYTHING that isnt just laying in bed, not to mention constant joint and muscle aches and nausea. it is so exhausting. i barely do anythign, i only work 20 hours per week.. i can function, but i just get worse and worse. im 19 and a girl so doctors never really hear me out i dont kno how to approach thm or be very assertive. does anyone here know how to be their own advocate? or anything? sorry for my spelling errors and confusing format lol!!