If you are late for your period, the only thing to do is take a test.

No method of birth control is 100% effective, so every time you have sex, pregnancy is a possibility.

Have you had unprotected sex before last wednesday?

nope i didn't have unprotected sex before ... and i just took a test it says negative ... i don't know what could be the problem because i'm never late

If last wednesday was the only time you had unprotected sex *if* you got pregnant from that you really couldn't get an accurate positive much soon than next wednesday. But since this incounter was after you were already late, I highly doubt that you are pregnant.