Why am I exhausted the week before my period?

Because the week before your period is the late luteal phase, and it is the point in the cycle where your hormones, your temperature and your sleep are all working against your energy at once. Tiredness in this window is one of the most commonly reported premenstrual symptoms, and for most women it is a normal part of the cycle rather than a sign that something is wrong.

Three things are happening at the same time.

• Progesterone rises and then falls. It peaks in the middle of the luteal phase and drops sharply in the days before bleeding starts. Progesterone has a sedating effect, so both the high and the withdrawal are felt.
• Oestrogen drops too. The fall in both hormones together is what the NHS and ACOG describe as the driver behind the cluster of premenstrual symptoms, of which tiredness is one.
• Your sleep gets worse even if your hours do not change. Core body temperature is slightly higher across the luteal phase, and reviews of sleep across the menstrual cycle find more disturbed sleep and poorer sleep quality in the days before a period. You can spend the same eight hours in bed and wake less restored.

There are two other explanations worth ruling out, because they are common and both are treatable.

• Low iron. Heavy periods are a frequent cause of iron deficiency anaemia, and tiredness is its main symptom. The clue is that the exhaustion does not lift once your period ends; it stays flat all month.
• Premenstrual dysphoric disorder (PMDD). A smaller number of women get premenstrual symptoms severe enough to disrupt work, study or relationships. That is a recognised condition with its own treatment, not something to push through.

What tends to help, in the ordinary sense rather than the medical one: keeping your sleep and wake times steady across the month rather than trying to catch up at the weekend, eating regularly, and moving even when you do not feel like it. Tracking matters too, because the single most useful thing you can tell a clinician is whether the tiredness is cyclical or constant.

Speak to a doctor if the tiredness does not lift after your period starts, if your bleeding is heavy enough that you are changing protection every hour or two, or if your premenstrual symptoms are severe enough to interfere with daily life. The NHS advice is to see a GP when symptoms affect your day to day or when lifestyle changes have not helped.