You can say "I got my period" or "My period started."
Here are some other ways to say it:
- I started my period.
- I'm on my period.
- My period came.
- I'm having my period.
You can also choose to be more specific about the time frame:
- My period started today.
- I got my period yesterday.
It's important to remember that everyone feels comfortable using different language when talking about their period. Choose what feels most natural and comfortable for you.