Do I take plan B

Hiii. So I just got off the implanon after 3 years. I went on the pill for like 3 months, it fucked with my mental health so I stopped taking it. I’ve had a widthdrawl bleed and that’s all- in a perfect world my period will start middle of next Monet but I’ve never had regular periods and I’ve just come off birth control so I highly doubt it.

My question is- I just had sex with my boyfriend. He didn’t finish in me (pulled out). Should I take plan B or am I already really unlikely to get pregs?