Plan B question

So I took plan B after the condom broke 2 days after my period and then 2 weeks later had my period again and haven't had it since around the 4th of July we have had unprotected/protected sex since then like he would pre cum inside of me but had the condom on before he actually came and I did take a pregnancy test after the pill and it was negative and I wasn't sure exactly when I had my period so I estimated it on here and I'm a week late to get my period acourding to this and my bf swears my boobs have been getting bigger and I told him its probably because my period is coming up I hope but he seats they have been for like 2 weeks and I've been getting back pain and pain in my side laltey and I know I'm probably not pregnant because I doubt anything like that would affect me that quick but does anyone know what could be the issue?