wheres my period gone?

okay so I don't feel any different I've took two pregnancy tests now. my periods are normally around 30 days apart but the 13th Marked the date I was supposed to start my period I didn't have a period in July so I'm two months late. i haven't had a period since June is this normal?...i don't think so.i took one tests the third week I missed my period and the second one two Friday's ago both came out negative so what's wrong with me?