Periods can be late for lots of reasons. Things like changes in routine, stress, illness,
weight gain or
loss, or just a blip in the hormones. Most women are occasionally late and periods don't always work like clockwork even if it's the norm for someone. Pregnancy tests are very accurate and symptoms of pregnancy are very much like symptoms of PMS. Also, if a women doesn't have enough hormones to trigger the pregnancy test, they don't enough to cause pregnancy symptoms.