For me it was during and after taking finasteride. So it was a side effect and it is a symptom of PFS, for me.
Everyone is different. For me it got better over time. Other symptoms did not.
One thing I know, focusing on it and being anxious about it will make fatigue worse. Find a way to relax, either on your own at home, using an app, using a medication short term, or going to therapy.