Why can't I get pregnant?

Iv been off birth control going on 7 months now and don't use protection during intercourse we have been trying to have a child for a while now and it's just not happening I have missed my first period this month and I never miss always on time I was supposed to start a week ago as of January 25th 2016 so I'm a week late now and I just took a pregnancy test that was negative. Should I take another one in a couple days am I possibly pregnant and its to early to tell ?