I realized that my low mood is caused by fatigue

I've been suffering from mood swings and being sensitive to stress for 4 years.

My psychiatrist said I don't fit a diagnosis but I take medicine to stabilize my mood.

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I'm also always very tired. I ride my bike 2 to 3 days a week for an hour so I don't think it's because I don't move enough.

When I go outside all day for a few days, I need to stay in bed for a day.

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I started CBT and I realized that my low mood is almost always caused by fatigue.

What should I do?

Would pacing work?

I feel like it's not about mental condition anymore.