could I be pregnant?

My fiancé and I use no form of protection, and he consistently never pulls out, so I took 4 home pregnancy tests 2 weeks ago, the day after my period was late and now it's going on week 3 and still no sign of a period. Are false negatives common? Or is there another reason I could be late? I'm not stressed and I have nothing else I can think of that could affect it.