We used a protection but period came earlier than it is supposed to

If I'm reading this correctly...
Your period started 2 days after you had sex? Or am I reading the dates wrong?

Regardless, it sounds like you need some reassurance. There's nothing to be afraid of - unless you think you're going through an unplanned pregnancy... otherwise - consult a doctor perhaps; take a test.

But if not, periods are... They kind of have their own mood swings. Sometimes they'll choose to come the first week of the month. The next month, it'll happen on the last week! At least that's how it is for some women.

Incorrect dates or assumptions shouldn't really be stressed over, unless there's some type of routine for your menstrual cycle. Still - I wouldn't worry about it if you're just stressing over the dates...

But maybe I'm still wrong or not understanding your question - if I am: my deepest apologies... but I hope you have gotten some kind of helpful information out of this (probably not...)

Sincerely,
Whomever I May be to You