its hard to say without having any info on your site or the site url. but in general, if your site is new and you have not been building links for at least 3+ months, then there could be a reason. google doesn't update backlinks everyday but does once in every 2-3 months update on backlinks. if you are searching with link: string, you will not not find any new links but google webmaster tool will show more accurate result so sign in to see whats there