If you have taken many tests, then you are probably not pregnant....at least for when you figured you had become pregnant. The hormones which make a pregnancy test positive don't take very long to appear.

At six weeks gestation, it would be very easy for a test to read positive. You do not always pass an egg every time you ovulate, so this may be why you think you might have become pregnant and aren't.

You may have become pregnant later than you thought, since you still seem to be experiencing some hormonal side effects. Give it another couple weeks and take another test if you have not menstruated.