What Causes Delayed Menstruation, Nausea And Frequent Urination?

It s been 38 days since my last period ended, I usually get my period about 28 days after the previous one has ended, so I m close to 10 days late now. I have literally been peeing every 10 minutes, and I feel a tad bit nauseas from time to time. I have taken 3 pregnancy tests (at home) and I have gotten all negative results. I m horribly confused and more than a bit concerned.