Had period . . . Could I still be pregnant?

On the May 19 my boyfriend and I had sex, the condom slipped off as he was pulling out. He hadn't come yet so there was no semen in the condom and about an inch of it was sticking out of me. We were confident that I hadn't been exposed to any speem but I took plan b just to be safe (36 hours after the incident). Then, June 3, right on time (28 days), I got my period. I had horrible menstral cramps the first day (not uncommon for me) and my period was very heavy, definitely not implantation bleeding. It was dark red but I did pass a blood clot that was almost the size of my palm but a little smaller. My period lasted for 4 days (4-5) is average for me. It was very heavy the first two days and then faded, which is also pretty normal. Now I'm scheduled to have my period in 8-9 days but I've been noticing some weird things. I don't think I'm having more cervical mucus, it's just different, very watery. Also the lower part of my abdomen is a little swollen. I'm very skinny, but some days it will look bigger than others. Yesterday I could hardly tell it was there, but today I think it looks huge. Other than that I haven't had any pregnancy symptoms. My breasts aren't sore and they are as tiny as never, my nipples also aren't any darker. I've felt a little nauseas this past week, but that happens to me when I'm nervous or upset, and I've been both lately. So does it sound like I could be pregnant? I've also been rather gassy lately, but I don't know if that's even related. Feedback would be appreciated since I'm freaking out.