plan b, implantation, or just period?

hi! july 17th my boyfriend and i had sex. we used a condom but midway through he pulled out and claimed that it broke. he told me he didn’t cum, but he wasn’t a hundred percent sure. i put a finger in, swabbed it around, and didn’t feel anything coming out either. the day after, july 18th, i took plan b. according to the app, my ov week is the 13-19.

i’ve been having back pain, some nausea, and a really big appetite since. last night i had a litle bit of brown discharge and spotting. i woke up with some red blood (will attach pictures). my period is not due until aug 1.

is this implantation, a sign of the plan b, or just my period? thanks!

also: the back ache is now moreso of a joint-hipcraming back ache thing...