I totally sympathise. I have always been a bit 'glass half full' but health anxiety would be fleeting. Now it dictates my life! I can have three/four serious illnesses before breakfast and my husband is getting sick of what he calls 'toothgate' [am obsessed by gum disease caused by receding gums, one tooth out already and implant pending...].
I deal with it by telling myself I am having a day off. Today is my birthday, so whilst am working at home [or wasting time on here!] I am having a day off from my health. My 40 or 45 year old self would find this absolutely pathetic, but it works for me.
I have a male friend who has been crippled by health anxiety to the extent where he can't take holidays. His wife insisted he paid for a full body scan check-up. Nothing was found - he was in great physical shape. Has it helped? Not really - he is now convinced they missed something or he was not tested for something rare he has got.
Distraction works for me - I can have a definite physical symptom that disappears when I am teaching, only to return the minute I think 'oh, that chest pain has gone'.
The power of the mind...