What “PMS” and how do i know if i have it ? And sex drive

I’m seventeen and My period always come between 19-21 days. But the cramps getting worse and I’m getting super tired each month. I have a strange sex drive, i used to want it all the time. Now i feel like my mind and my lady part are two different person. Brain 🧠 said yes while the vangia said nah maybe later. Can anyone explain that ?