you might have to factor in the period. It never fails for me that the day before my period I'm spent. No energy. For some weird reason my period showed up a week early last time. it was race day. I had no idea why I was so tired through the swim and wanted to sleep on the run (it was an olympic distance race). The next day I got my period. My period is usually very regular and I'm on a hormonal BC so it should be regular, but for some reason it wasn't, not that I can plan for that, but it reiterated the fact that the day before I'm tired. I don't swim the day before because I just get frustrated with feeling tired, I usually just do an easy run and/or an easy ride where I don't look at pace/watts.

People are different but I know quite a few women who have the same issue I have the day before the period or the first day. Usually after that everything is fine, so you might not have to take the whole week into consideration, but there might be a day or two to plan for. You don't want to waste a day trying to do a hard workout when you know you probably can't, use that as active recovery.