... or discharge?

I had sex in mid/late June and after I took Plan B, I had a 2 day period and then it stopped. I've missed what regularly would've been two periods. I was already very irregular and had just started to get a normal period when I took Plan B. I am very slender and feel that if I was pregnant, I would be showing by now, but my breasts and nipples have been very tender that past 2 weeks. I am not nor have I ever been on birth control if that helps.