seems Facebook changed the result of posts, few weeks ago it was possible to read the comment count from the post directly
https://graph.facebook.com/125909647492772_502
I was having same problem, just adding likes.summary(true),comments.summary(true)
in parameter in against "fields" worked for me.
e.g. I used https://graph.facebook.com/me/feed?access_token=ACCESS_TOKEN&fields=story,from,story_tags,likes.summary(true),comments.summary(true)
instead of https://graph.facebook.com/me/feed?access_token=ACCESS_TOKEN
Also you can add other parameters if you want; separated by a ,