HELP! Could I be pregnant?

Currently 8 days late for my period, usually it's like clockwork. I've taken three tests (4 days, 5 days, and 7 days late), all negative. I'm not under any unusual stress, no change in routine, and all I've had are my usual allergies. What's the likelihood that I'm actually pregnant? Has anyone had this happen, and if so were you pregnant or did your period eventually come?