It's normal to have a tiredness peak during the day but if folk are out at work they can't do much about it and by 3pm, depending on the nature of their job, going home time may not be that far off. That's why firms have breaks - a decent one for lunch where you can eat well, coffee and tea break morning and afternoon. There are those who work through but most people need a bit of time plus food and drink to refresh themselves.
When I was on a day off during the week, if I had nowhere to go or anyone to see, I always had an afternoon nap and felt better for it. At work I was fine because there were so many distractions.
Being at home and working alone means you organise the day how you want and you may not by nature have a great deal of organisation without a structure, colleagues, etc.
It could just be that, op, and nothing to do with perimenopause if you have no other symptoms. If you do start going out to work again you may be different.
There are those who thrive on working from home. Someone close to me does a tremendous amount of creative work in the middle of the night, while the rest of the world sleeps, and sleeps part of the day, making appointments for telephone calls/conferences or (now) meet ups, in advance.
It's marvellous that you sleep well at night, be grateful for that. Eat well, make sure you have sufficient vitamins and minerals and hang on because, whatever this is about, it will pass.