I had unprotected sex the day i got my birth control shot i took a plan b the next day , how effective is the plan b in this case ? my last period was on 1/15/2021?

Plan B: Plan B is a form of emergency contraception. It prevents pregnancy from occuring when there is no established pregnancy. Plan B is not 100% effective. No medication is 100% effective. According to plan B, efficacy ranges between 75-89%, more effective if taken sooner than later. I would follow your doctor's and/or Plan B pamphlet instructions. If there is no period in 3 wks, get pregnancy test.