What Causes Late Periods, Cramps And Negative EPT?

I am 8 days late for my period I have took 3 ept test which all said negative. I have been having cramps like I normally as if I was going to come on my period. I have been under alot of stress working full time And going to school full time I have a 3 year old son that I also take care of. I don't get much sleep, and I have a poor diet. Some days I might eat alot And other days won't really eat much. I should have came on my period April 5th and it is April 13