Couple wild-ass guesses:
- What temperature did you mash at, for how long? Have you calibrated your thermometer by making sure it reads 32 in icewater and 212 in boiling? Could be starch haze if you're mashing too cool or too fast and not getting full conversion.
- How vigorous is your boil, and how quick do you chill? Could be hot break if you're stuck on a kitchen stove that can't quite bring six or seven gallons to a full, rolling boil, or cold break if you're taking too long to chill (though, for the latter, I've had chills that took an hour to get down to pitching temp and still cleared just fine, so, "too long" is probably at least a couple hours).
- How long has it been total? Another 1.5 to 2 weeks after just one week is 2.5 to 3 weeks -- you'll still get significant clearing if you go out to four or five weeks. Another 1.5 to 2 weeks after a month, you're getting into the territory of diminishing returns.