breakthrough bleeding months after taking plan b?

is it possible? i took a plan b a few months ago, worked obviously, and i had my period like a week after that (which was irregular bc my period wasn’t due for another 3 weeks) and then after that i got my normal period within my 30ish day cycle. now it’s been a few months later, 2 normal cycles later, just got off my period 2 weeks or so ago and i’m having spurts of bleeding. the blood started lighter brown but it’s turn to dark brown and slightly more heavier amounts. but it’s not like a period. i’ll bleed some and then it’ll stop, and start again. it’s been happening for like 5 days now and i’m so confused. i took a pregnancy test too and it was negative. i’m just confused what’s going on with my body because my cycles are pretty regular but the only thing i can think of that’s caused it was the plan b that i took a few months ago. thoughts? (also, i’m not on any form of birth control.)