Is the keg cold when you take the sample (I'm assuming not since you're naturally carbing)? If not, the pressure is a lot higher at room temp and the CO2 won't be in solution, giving you a foamy pour. How long is your beer line?
Cold keg, 6'-8' beer line, it should be a lot better. If you have a way to check the pressure in the keg, a gauge, 30 psi at room temp is pretty good.
That being said, in your case, 2 weeks, it may be done or it may need more time. I use a bleeder valve whenever I naturally carb in a keg. I can monitor the pressure buildup, bleed off any over 30 psi at room temp, and wait until it stabilizes to know it's done.