PMS and period talk

Supposedly PMS starts the week before your period and ends when you start your period. At least that’s what I’ve heard all my life. And PMS comes with mood swings, tiredness, feeling blah, all that... well, is it possible for PMS to start when your period starts? Because I’ve always felt normal the week before my period but all these things hit after I start. I get so tired and hungry and just don’t feel myself. Anyone else experience this?