Mood shifting in the days before a period is common, well documented, and genuinely hormonal — that much of the saying is true.
What the saying does is close the conversation. When low mood, irritability or anxiety before a period is severe enough to damage relationships or make work impossible, and it lifts once bleeding starts, that pattern has a name: premenstrual dysphoric disorder.
PMDD affects a small but significant minority of women and is a recognised condition with recognised treatments. It is not an extreme end of ordinary PMS to be endured.
Tracking symptoms against your cycle for two or three months is the single most useful thing you can bring to a doctor — the pattern is the diagnosis.