idk what this is

so i started birth control a month ago, one of the days i was rlly late taking it two days in a row and had unprotected sex with my bt and he did not pull out. before i started birthcontrol we also had unprotected sex (he did pull out those times). I took a plan b and continued birth control. when it came to the placebo pills i took those to make sure id get my period but it came later than i thought so i took a pregnancy test(yesterday) and it was negative. today i got my period but it was different than normal. A lot more pain and i bled out chunks of tissue. It looks exactly like google images of 4week miscarriages. what could it be? i think i would of tested positive if it was a miscarriage but ive never had this before