spotting?

i had sex on the last day of my period (saturday) and then took a plan b sunday just in case. it’s now thursday, and i’m having some light red spotting and little clots. it’s day 10 of my cycle. cycle is usually 25 days long, i don’t know if i should be worried about pregnancy or if it’s from the plan b or what. i haven’t taken a plan b in a while but i think i remember the same thing happening before?