I'm 4 days late on my period don't think im pregnant what could it mean?

Cycle variation. Probably it is just a variation of your period cycle. Just wait for couple more days.
Are you sure? Pregnancy is a very common reason for a missed period. If you haven't already, you might consider taking a home pregnancy test. If the test is negative and your period doesn't come in the next few days, you could visit a doctor to see what's going on.