Hi Rosa,
I am so sorry about your loss. I have had a miscarriage at 13weeks in July. The baby had trisomy 18 (3 of the 18th chromosome) which is not compatible with life. I knew nothing about it and had never heard of it... After some investigation we went to a genetic councelor who was able to give us all the answers I needed. There is a whole lot of different trisomies and maybe find out the details from your obs and ask him if he (or your GP) can refer you to a clinical genetics service in Perth. The service here in Melbourne was free of charge.
Don't worry too much, chances are that your risk of this happening again are just the same as for any other woman within your age group. I know exactly how you feel, I was so confused as well, but the genetics services really helped me to get my head around all this.
Hope this helps and big hugs.