Period a week late

my period is a week late, supposed to start 11/13/17 and i usually get it every 5 weeks, a 35 day cycle. i have unprotected sex using the withdrawl method everytime i have sex, which is about twice a week. my boyfriend has only came in me one time that i know of, and it was the 27th day of my cycle. my periods are never late and ive been feeling tired, nauseous, and moody. i took two pregnancy tests but they both came out negative, but i read online drinking too much water can dilute your urine and give a false negative. i drink about 10 bottle a day at least, no joke. could i have gotten a false negative on both tests? should i stop drinking so much water and take another test? im only 17 and im really scared.