Hi, with my first m/c I had no symptoms at all, I just started bleeding with cramps and it was all over within a day, this was about 7 years ago.
With my recent 4 m/c's (in past 12 months) I always get the same symptoms, which is sort of how I know what's going to happen.
Awful backache, more like a sciatic pain, as it tends to shoot down my left leg and sometimes it unbearable to walk, this generally goes on for a couple of days before I get the brown spotting and discharge (sorry if tmi).
I generally also get the feeling that I am no longer pregnant, more like an intuition really.
Hope this helps x.