I would give it a few more days, until your AF is due before testing again.

I can't comment on the Crystal Clear as I have never used them, but different HPT's measure different amounts of HCG, and being 4 days you may need to wait longer before a HPT would show up as a positive.

Usually if there is colour to the line that is more indicative of a positive test, a clear line is usually an evap line, so not positive, the line needs to have colour to it.

HTH's