Your first couple years of your period will not usually be on the same days. For example mine started on a 1 then ended in a 6. Then it had different numbers and now it starts at 26 and ends on the 29 or 30. But if you just started the past couple years then they won't always be on the date you expect. So always be on the look out for signs.
Yes I always keep track of the start date
How do you know it's early? Are you keeping track of the start dates? You should be tracking the start and stop dates either on a regular calendar (I used to write a star on those days) or you can be more modern and download an app on your smartphone to track it. There are tons of them on the app store and they are mostly free to download and use.