pregnant? young? sos

I had unprotected sex, about a month ago, I took the morning after pill the next day. My period was 6 days ago, and it came 3 days late, it started off light on the first day, but by the next 3 it was very very heavy. I thought I was spotting at first but by how extremely heavy it was it was not spotting. It’s been over now for 6 days and I am in my ovulation window again, but my boobs are still sore like how they are on my period, idk if this is because I am pregnant or ovulating? Or maybe it’s still a side effect from plan B? I took a test when I missed my period but it came up negative then I got my period the next day. I want to test again but I am scared to buy it at check out, the only reason I tested the first time is because my friend checked out for me. Can someone tell me or help me with this