Could I be pregnant

My last period was June 23rd thru 28th.. I was suppose to started July 22nd and still nothing.(which makes me 5 days late) But I took 3 pregnancy test all three said negative. I have even checked my hgc level at work since I work at a hospital and it was high. I have had sore breast for about a week now. Today I have been sleeping on and off like crazy. I don't know if its because my daughter is not home and I can finally rest?! Also I have lower back pain. So my question is when should I test again to see if I'm pregnant or not?!