Pregnancy Test

I have taken 4 pregnancy test and all have come back negative! I am a week and a half late! I have been very stressed lately due to a break up and helping him get out of my house. Can stress make you this late! I'm freaking out even though all the prenancy tests are negative. Should I take another test again? I took one yesturday and it said negative as well! I use the diaphragm and condoms. I had not scares with the condom breaking or anything. Help! Someone help me feel at ease!