Implantation and cramping

Hi there, I realise this is probably a similar question to many other peoples, but I would just like some advice specific to me.
At the begining of september (started on the 3rd) I had an early miscarriage.
My period returned on 28th September, then my next period was only 3 weeks 2 days later on the 22nd october. My normal cycle is 28 days.
I have had unprotected sex just once on November 5th, which according to the charts, was my most fertile day - going by my "normal" 28 day cycle. Keeping up ? lol
My period is due on 19th November. But yesterday I started having tummy cramps and aching. Today tiny amount of spotting, hardly anything. Last time I had implantation bleeding.
Could I be lucky enough to be pregnant after just having sex once? Could it be another early period because my body is still messed up? Are my chances of a miscarriage increased after last time? Is there anything I can do to help prevent miscarriage? I dont drink or smoke, i go the gym, i eat healthy foods, although I'm a vaggie. Any ideas?

Please give me your thoughts
Many thanks