My ex and my daughter in law, took more than one test befiore they got a positive. That drove us to distraction seeing as she was so overdue.
Don't stress about it, it has been said that if you are stressed, generally your body has a fight or flight reaction where if you are not in a settled state as a reaction to your environment, your body will resist your efforts to get pregnant. You can see where that makes some sense, i don't know if it works though, but there's no harm in chilling out a bit.