I need help please!

Hello all,
I'm 19 and my boyfriend is in the military so I don't see him but every 6 months or so. The most recent time I was with him was before Christmas, and we were having sex without a condom and he came inside of me. It was a dumb choice because I'm not on birth control, and I took the plan B pill the next day.
Now a month later I'm 3 days late for my period, my breasts are tender like the would be when on my period, and I'm having a lot of clear discharge.
I'm really trying not to panic, but should I be worried? Should I take a pregnancy test? Or is this just the plan B pill messing with my hormones? 
Any comments or opinions would be greatly appreciated!