Bleeding at 7 weeks pregnant

Hi I was wondering if anyone had such a thing happen. I have been bleeding for the past 4 days, first just a little spotting, but today a proper period-like bleed. I had a scan this morn presuming i was miscarrying as i have had one before, however to my delight and confusion, all is well and baby is perfect, scan showed no trace of a bleed. Im so confused as to why im bleeding still if it doesnt even come up in a scan, then why the blood?? I have 2 kids already and never experienced this before, im nervous and im aware if i continue to bleed, they will scan me again next week but doc told me not to worry that all looks perfect, but why the blood then!! Wish i could relax