Plan B - late period.

Lizzy
On May 6 my boyfriend and I had unprotected sex. (I had just ended my period on May 4 and had started it on April 31.) So on May 5 I took Plan B, only to have another period on May 14 that lasted for about one week. 
So I didn't have my regular period at the end of the month in May. And it's been a month since I had the random second period on the 14. I took a pregnancy test two days ago just in case and it came back negative. 
I still have yet to have my period and I don't know for sure if it's late just because I'm stressing about it or if the Plan B messed up the hormone balance. Any ideas? Thanks.