Some one who has a normal cycle would need to wait 2 weeks. That is when thier period would be due. So if you ovulated on the Feb 14 and you have a 28 cycle your next period should be on Feb 28th. That would be the best time to take the test.
What you are experiianing could be implantation bleeding. That usual occures 7 - 10 days after conception.
Your best bet is wait till you miss your period to take a test. And get the double pack just to be sure. Take one first day of your missed period and take the second the next or even 2 days later.