thoughts on pregnancy tests?

So we have been trying for baby #2.. My period is over a week late and every brand of pregnancy test I have taken says not pregnant. I woke up today with extreme nausea (like I did when I was pregnant). Nothing else is going on cramps etc. just a little confused. I even took a pregnancy test last night which said negative. Thoughts? When I found out I was pregnant with my son I took at home pregnancy tests they were positive.