Hurt when husband keeps saying no to sex while TTC

It's crazy that i feel so hurt and disturbed by this.  i get it we have been together for 6 yrs, married for almost 2.  We both finished our graduate studies, and talked about how we are ready to start a family.  We're busy, our work hours are not normal, we do shift work so there are days when we only see other for 1-2 hours before one of us has to leave for work.  So on those precious hours, why does he say no to sex during my fertile window?!  I feel hurt, unwanted and I don't know what to do.  I know we love each other but why is our libido so low?  Has this happened to you?  Any help or advice would be appreciated!