Day 4 of missed period...

Today is day 4 of what should be my period. I still have not started and my periods since I started when I was 13 are ALWAYS regular. I'm really hoping this is it. We have been trying to conceive for 8 months and I have already taken 4 test and all were negative. Any advice? Is it possible its to early to tell? I mean I have no faint line, nothing. And when should I test again?