No period..

My period is a month late now, we have been trying to get pregnant for months now, with nothing.. I am usually on time. At about two days late I took a test and it was negative, a couple days later I took another.. Negative. Well now it has been a month and still nothing! No tenderness, no sort of sickness and NO SIGN of my period. I feel no different so I don't think I'm pregnant (although I wish I was) but why would I be so late? Any logical ideas?