your symptoms may be part of premenstrual syndrome
as menstrual cycles can change due to many causes, so this delay in your periods may be because of hormonal changes etc,
if there is unprotected intercourse
around the time of ovulation in previous cycle then there is possibility for pregnancy, sometimes urine pregnancy test kits may not detect early pregnancy.
one more possibility is pelvic inflammatory disease
so you better consult gynecologist and undergo physical examination and ultrasound
examination to detect the possible cause of your problem and treatment can be taken accordingly.