Hard to put a finger on "extreme fatigue" ........ I get that you always "listen to your body" and now you think you have a problem because your "tiredness level" doesn't match expectations.
A good way of avoiding this kind of worry and or disappointment is to actively monitor your abilities with measuring devices.
A clock and an odometer is enough, a HR monitor can help as well. Things like a scale, and a BP monitor can also reveal variability in your day to day or week to week fitness and health.
I've been measuring my efforts with devices for 40 years. I established baselines and maximums for HR. I tracked and recorded weight and power output using devices that could repeat exact performance levels.
Without piecing together the true volume and intensity of your exercise performance and meshing that activity with other life stresses or personal habits - its really hard to say what's going on.
I guess a stress test is an idea, but an echo cardiogram and EKG is the more natural starting point. (along with blood test)
Hope you get to feeling better - but don't compound your problems by stressing about your fatigue.
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