Confused

I took plan b in the beginning of the month and then bled for two days weird brown bleeding. I also had cramps with that bleeding. My boobs have been sore and were really sore in the middle of the month but now aren't as sore. I still don't have my actual period. I did take a pregnancy test 21 days after sex and it came back negative. Should I test again if my period doesn't come? Do you think I tested to early?