Delayed Period, Sore Breasts, Stressed. Pregnancy Test Is Negative. What Is Going On?

hi im supposed to have my period on may 27th, however, up until now i still don't have my period. i had sex somewhere on may 8th to 10th. my last period was on april 27th and lasted for only 3 days. i experienced sore breast and light pelvic pain since yesterday june 2. there was no spotting or discharge. i don't feel tired nor urinate frequently and not picky on foods. im goin through stress from school and at home, im also doing work outs for the past few weeks, and i just had my vacation a week ago. i have done a test 7 days after my expected period but it came out negative.