Pregnancy is tested by the presence of a hormone called hCG in urine or blood. This hormone is secreted by the chorion of the fertilized egg and later by the placenta. Egg after fertilization can take 12-14 days to implant in the uterus. Ideally, pregnancy test should be used on the missing date of periods. Pregnancy test can be done after 12-14 days of conception. When this conception took place, no body knows, so, it is better to wait for due dates of periods and get test if no periods.
Wait until your next period. If it doesn't come test the next day in the morning... I did that with my 4th. I didn't start on the 18th so I tested on the 19th and positive. Good luck to you if your ttc