@Pommy8. @Edithead - that's a bummer ... as @Afraser suggests - definitely raise the issue with your GP and Onc - and ask for a full body check up - full bloods, heart & liver function, diabetes, electrolyte levels (salts & minerals in the blood - fatigue is common if levels are low) ....get everything checked ...
Maybe even request an ECG & a stress test - so you have a 'picture' of how things are now, to compare with others further down the line. Were either of you on chemo? If yes, Which one? Sadly, some are known to cause heart issues further down the track :(
Keep a list of how it is affecting you to take to your appointments & take care xx