you can test now using first response (they detect hcg & hcg-h. hcg-h is the hormone produced before hcg so the test is more accurate and can tell you sooner. for more accurate results test day of your missed period & again 5 days later if necessary.)
you should probably wait a until you're a week late maybe even more. it took a friend of mine a month of being late to turn positive! i know you really want to know now but you could be getting a false reading.