Help Please

Tenee

How are you guys this is my first time posting so I’m really nervous. Could I be pregnant? Took an plan b and I missed my period by one day. I know that could be a sign affect of the pill but..... I took a test this morning and I think it was positive. Should I retest tomorrow? And also how could I be if I took the plan b right after??! Doesn’t it supposed to stop Ovulation/fertilization??