Unprotected Sex Stress

The SO and I have been using the pull out method, which he's been pretty damn good at- until yesterday. We were going much longer than usual when suddenly he came inside me with no warning- to me or himself apparently. Yesterday was the last day of my period so I know the chances of pregnancy are on the rise which I think might be what's causing me to be so nauseous right now. I know stress can effect periods so I don't know at what point it's acceptable to get worried. I also have no idea when I should take a pregnancy test, should I just wait for when my next period is supposed to start?