plan b

so, i’m on the birth control pills, but had to take an antibiotic to get rid of a strep-throat -like illness. i had unprotected sex 6 days after i finished my antibiotics, so a day before my birth control pills would be fully effective. i was uneasy after, so i took a plan b. my period was 1 day late & extremely light, like i don’t know if i can even consider it my period. it’s like a light brownish color. is this normal? is this because of plan b?