Should I test ?

Hi everybody I need advice. My period is synced to my sister in law’s since we live in the same house. Every times she gets it I either get it the same day or the day after but usually a couple of hours after she gets it. The thing is that this time she got her period and I haven’t gotten mine. It’s been 4 days. According to the app I get my period tomorrow but the app is never correct about when I get my period. Should I take a pregnancy test or should I wait a couple of more days to see if it will come. ? I should add that I’m on the pill.