I lost all my "groups" in my address book when I did the El Capitan update.

I did the El Capitan update yesterday. When I started my computer today I found that all my addresses were gone. Then I was able to finally get them back - but instead of one address per entry I now have TWO. AND all my groups are still gone. This address book is the most important part of my computer and I need it to be back the way it was. I have over 3000 addresses in my address book (now 6000+!!) and over 100 different groups - I can not replicate these again. PLEASE help me fix this.