oh em i only just read this for some reason i thought it was from your previous loss, so sorry!

I am glad your u/s's have gone well and bubs has a nice heartbeat, fingers crossed you are just one of those people who tend to bleed for no particular reason throughout pregnancy.

Not sure if this will help but ive done some research when i was in denial about my m/c last month and here are a few of the suprisinly many reasons bleeding may occur in early pregnancy:
your body sometimes actually continues to have periods when pregnant in some women
an undetected UTI which is becoming more aggressive due to pregnancy
irritation of the cervix
Postcoital bleeding is vaginal bleeding after sexual intercourse. It may be normal during pregnancy

HTH put your mind at ease a little