Why Are My Menses 3 Months Late?

my husband and i just recently started wanting to have a baby. I am almost 3 months late on my period, in the past i have been irregular on my periods, but have been regular for almost 2 years now until now, I have taken about 4 at home pregnancy tests, and they are all negative, but lately I have been very thirsty and have had headaches everyday for about a week now. What does this mean?