Pregnancy or Switching Pills?

I began taking a "one period every 3 months" birth control in June & stopped taking the traditional form. I have not had my period & but had been nauseous. I took two pregnancy tests 4 days apart and both were negative. Since then, I have received spotting, cramping, breast tenderness, etc. as if I was supossed to have my period. Now I received a yeast infection which I read is another sign of pregnancy.