I haven't had a normal period since sometime in May, I took a home pregnancy test in June and another in July and they both came back negative. Now that August is here I have become more tired and a little naueous, and a bit constipated,if I am not pregnant what is causing my period not to show

If you are not pregnant and you haven't had their period in a while, then I suggest to go to a doctor to see if anything is wrong. Sometimes when women don't get their period for a while and they are positive that they are not pregnant, it means that something is wrong inside them. I suggest to go to a doctor just to see what is happening and get the correct answer. Good luck. :)