What Causes Headaches, Lower Back Aches And Nausea While HPT Is Negative?

Hi my name is Isabel, i am 26 years old and had a tubal ligation in 2013. My last period was on 1-3-2015. Since then i haven t had a another one and have been feeling sick lately,with headaches, lower back aches, tired and sleepiness and some nausea to some foods smells. I took a home pregnacy test and it came up negative.,what is happening to me?