Plan B side effects

I’m 18 and I took Plan B for the first time a month ago. It was after my first time having sex and we used protection but I just wanted to be extra cautious since I’m not on birth control. I got the pill, and I had some side effects like nausea and cramping within 24 hours of taking it. Two weeks ago I noticed my breast seemed bigger and sore, this made me so nervous but my period came a week early and very heavy so I felt like I was in the clear. My breast still feel heavy and sore, I’m not sure if it’s the hormones or what. My school doesn’t have sex ed so I’m a little naive on this subject but is there any possibility I could be pregnant? Or is this just normal effects of plan b? Thank you so much for answering💖