I don't know whether I'm on my period or not and I'm freaking out

So I am usually all about being on time with my period. I was due to start it yesterday, and I did start to have some spotting and brownish discharge. It wasn't enough for me to need a tampon really, but I put one in anyway.  When I removed it, it wasn't very saturated but there was some bright red blood on it.  Today it's the same kind of thing. I have red blood, but not much and a little bit of the brown discharge... but NO cramps. Usually I cramp like crazy on the second day and am pretty heavy.

I could just be being paranoid, but me and my boyfriend had sex on the 20th and the condom broke. I had started my last period on April 4th so I was scared because they say you ovulate around 14 days after you start your period.  So I went and got Plan B as soon as I had the chance which was about 48 hours after that. You can take it up to 72 hours after.  I do NOT have any symptoms of pregnancy, no fatigue, dizziness, nausia, swollen breasts... nothing.

Also, I am finishing up school and finals are this week. So I'm stressing. I HAVE missed periods before due to stress.  Also, I'm stressed about my Birthday and turning 25. :(  Please let me know what you think. If you think I should take a pregnancy test I will do so... I took a pregnancy test last week because I was feeling paranoid too but it was about 4 days before I was due to have my period and the test came out negative. It's just weird that I do have a fair amount of red blood and brown discharge, but NO cramps!