A Few Weeks Ago I Had Sex, I Guess The

A few weeks ago I had sex, I guess the condom broke, the next day I took plan b. Then, 2 weeks later I had a super light flow and only saw blood when I peed, then nothing for 5 days, and now for the past 5 days or so I'm back to a light flow only when i pee. I also haven't had cramps or anything, and I usually cramp badly. I took a pregnancy test, just out of paranoia and it was negative. Is this just an effect of plan b?