Bleeding w/ successful pregnancy

I've been spotting/bleeding throughout my entire first trimester. I'm currently 6 weeks, 6 days. Never anything more than a couple drops in my panties and really only noticeable when I wipe. But sometimes it does get heavier on the toilet paper. It varies in color from brown (primarily) to pink and once it was even red. Doctors say everything looks good (been to the ER twice) and my hcg levels are continuing to increase. My question is does anyone know someone who had "breakthrough" bleeding throughout their first trimester and still carried their baby full term!? I'm so worried my body is trying to miscarry.