current_post not working – give me -1 for every post

What you are seeing is totally expected as you are trying to get the value of $current_post outside the loop. Before and after the loop, the value of $current_post will always be set to -1.

To get the proper value, you need to check $current_post inside the loop, the first post will be 0 and this will increase by one on every iteration of the loop.

For more info on creating the Post X of Y thing, check out these site searches on this issue