pac pvc tiredness lethargic

like all of you good people I have been suffering from
PAC PVC  since the age of 17. I am now 53.
initially not knowing what they were I constantly lived in fear. When I finally discovered what it was
I felt much better and  that was when I was in my late 20ties.
Always done lots of sport since my teens and never had PAC PVC
during exercises until I reached my 40ties.
from than on I get them during and after excercises
but kept going with sport . But in the last 2 years
my stamina and strength has decline despite
cycling for hours at a time.
It has now come the point when I cant do no more, due
to being too exhausted after  short  excersise.
After hundreds of tests blood,xrays, ecg, 48 Holter
Monitors all coming back normal with exception of
Holter showing some runs of PAC and  non sustained SVT.
I even bought an ecg machine and test myself regularly
When I feel exhausted but all seems ok even a cardiologist
Confirmed this/so I still don’t know whats the problem.
I wish I was still feeling the same as when |I was in my 20ties with PAC and PVC but in good strength.

Do any of you  have noticed a change  in the way they
Feel  ie:’ getting PAC etc and deterioration in stamina , strength,  , out of breath easily and feeling weak and lethargic like I do ? your repsonse is much appreciated