Hugs hun,
I had bleeding in both my pregnancies, with Charlotte at 36 weeks and 40 + they could never really tell what set it off, and with George at 6 weeks, they had a feeling it was implantation or bruising in my womb, but never totally diagnosed it.
If all the tests came back good, then that is a good thing. Try to just look forward and try not to get yourself worried about it. (Easier said than done I know).
Take care xx