Random bleeding in 2nd trimester?

I started bleeding one night at 14 weeks pregnant, not bright red, more like rust colored. Went to the ER the next day, and everything looked fine. Followed up with OB the next morning and found out I was having twins!! Long story short, everything looks fine, babies are healthy and the last ultrasound showed no active bleeding. Doctor can't tell me where it came from, but it's been two weeks now and I'm STILL spotting brown blood. I'm so ready for it to stop, even though I know everything's fine it still makes me nervous. Anyone else experience this that could help ease my mind? Thanks!