Did i miscarry a twin maybe or implantation

My daughter was conceived around May 2nd 2015 and i had a heavy bleed for 4 days with clots May 22nd it started. I didnt find out i was pregnant until end of June and shes a healthy 18 month old now but ive often wondered...a bleed around 4 weeks gestation that lasts 4 days with clots... would that be implantation or twins? Or is that common

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