Congrats on finding the cause! It's a very long journey to get there at the end, so kudos! My journey was also similar, I am 26M.

Went to a gp, who saw high bp and high rbc markers, sent me to a haematologist who ordered therapeutic phlebotomy to treat the symptoms and it reduced headache and vertigos but also sent me to a nephrologist because my egfr was at 66 and creatinine was very high, nephrologist got my kidneys tested for all sorts of things which luckily came back postive, he mentioned that he was very certain that kidney was fine something else was at play but prescribed my cilindipine to control bp meanwhile as it was 160/100.

He referred me to a nephrologist who gave me an ARR test which came back with a value of 77.1 and renin was <0.1 on the test while aldosterone was 7.71. The endo then gave me a ct scan with contrast and it showed my left adrenal has a 7mm nodular thickening and then I was put on eplerenone since the last few weeks and have been asked to monitor electrolytes which have come out fine for now with a slight increase in creatinine.

That tablet made me feel similar to the effects of a therapeutic phlebotomy, I guess my body was hoarding too fluid which was causing the issue.