Back-story is essential to motivate the plot and storyline of a novel.
It adds flesh to the main character/characters.
The placement of Back-story will vary according the genre of a novel.
The back-story of my protagonist started on Page 43 of my chivalric romance.
Did your Back-story start at the beginning or after numerous chapters?
In the drafts of stories I've done I have always placed a back story a chapter or two in. I think it's better this way, though I have read stories that have them at the beginning. It's just personal preference. What ever feels best for you.