Since your late, you can take a test now and get an accurate enough answer, just be sure to use first morning urine as it's most accurate for detecting the pregnancy hormone hcg. If it's negative and you still haven't seen your period in another few weeks, go see your doctor. If you're not trying to conceive, you need to using protection and/or birth control at all times.
I would just wait and see, if ur period doesnt start by the end of this week then take a pt. Keep us updated.