how do i know if i just had a miscarriage. i am a teen and my last period was very light and shorter than usual. this month my period was 7 days late and then last night i started to bleed lightly. this morning i changed my tampon and 15-30 minutes after i was bleeding so bad that it was running very where and so i went to change my tampon and a blood clot came out the size of my fist.( this has never happens before and i’ve been having my weird for 7 years.)