pregnancy tests are pretty accurate after a few days...
Have you had any symptoms that you're about to get youor period? ie swollen or tender breasts..
Stressing over it (and if you've taken 4 pregnancy tests, I'd guess you're stressing a little) can also cause it to be delayed.
A woman's cycle is an odd thing - anything can cause it to be irregular... exercise, change in
diet, change in weight, change,
stress...
Going to the doctor or planned parenthood for a blood test will answer your question once and for all...
