Anyone else have this experience?

S
So, I know that you are not doctors or nurses, however I'm just wondering if any other ladies have had this experience and whether they ever found out what it was:
I am 17wks4days and for the last 4 weeks I have had on and off bleeding and spotting - I have been to the doctors and have had an ultrasound, swabs, and bloodwork. All my labs were good, the placenta is good, the amniotic fluid was great, there are no ruptures or tears, my cervix is closed, and I don't have any bacterial infections.
Has anyone had this before? Did you ever get to the bottom of the bleeding or spotting?