Nausea, fatigue, and headaches are NOT early symptoms associated with pregnancy. The only "pregnancy symptom" you've had so far is a late menstrual period.
But a period that is only 4 days "late" is NOT a missed period. No woman ever has periods that are always 28 days apart, like clockwork. The date can vary up to 3 to 4 days (early or late) every month, depending upon how many days there were in the previous month.
You can take a pregnancy test the day after you miss a ;period. But, to be most accurate, you should wait until your period is at least 1-1/2 weeks overdue.