Ay, possible talaga kasi conception doesn't always happen right away, some of my mum friends got pregnant from timing na parang imposible on paper! That said, 5 days bago ang period is cutting it super close, pero if your cycle is irregular or if you ovulated later than usual, it's not impossible, honestly. Best way to find out is to take a pregnancy test (kahit negative, retest after a few days) or check in with your OB para ma-confirm kung ano talaga ang nangyari sa cycle mo, they can explain your pattern better than guessing! How are you feeling otherwise?