3 Weeks Late Exactly

Cortnie
I'm 3 weeks late today, So that'll mean I'm 7 weeks pregnant today if I am pregnant. I took a clearblue plus today and it said negative. I think. 
A coworker told me 3 weeks late is still a little to earlier to get a positive. She got hers at 4 weeks late. Could it be to early to get my positive?