How many days late can your period be before you start to worry? I'm always every 22 days, but now it's day 27.

Up to a week. Periods can vary somewhat and sometimes be later due to illness, travel, weight changes, a lot of exercise, etc. If you have had unprotected sex during your most fertile period (from about day 5 to day 11 of your last cycle), then you should start checking your pregnancy test starting on day 29, particularly if you have nausea, nipple tenderness, frequent urination, or fatigue .
2–3 days. If you have regular periods, a positive pregnancy test could be possible 2-3 days after a missed menses. Other common causes are delayed ovulation.