Hi Silverberry,
Just to say of my own experience, that being peri my own natural cycle definitely does 'interfere' with my being exceptionally tired. In the week or So before my period is due ( on mirena coil, so no bleeds but some pms symptoms) I can have a massive dip in energy levels at this point and my moods are horrendous,but let's not go there.. Can feel like I am swimming through mud, so tired and mentally sluggish.
So maybe worth a mood diary to see if you notice any cyclical changes at the same time each month that affect this worsening tirdeness? Whilst not a way to help it, it may benefit you to expect this rhythm if this is the same case for you. I use a mood diary to help me note a pattern.
Take care