What Causes Bleeding Without Pain?

hello...nom im 5th day period....2 months married....1st month married..then i was period 2 weeks early then suspected...but not like normal period...no blood cloth...so i thought it may be implantation bleeding cos not really pain n last after 5days n very light period....but then...2 weeks also b4 my period....then im now having heavy period....a lot of blood cloth....at the second n 3rd day...n stil having it rite now..but only a bit blood cloth....already went to clinic...but the doc scan n nothing is inside my womb...so please advise me