I'm not sure what you mean by "clean." Paxil, or Seroxat, is very very hard for most people to stop taking without withdrawal problems, so you taper off of it as slowly as you need to. But if you've stopped and you feel fine, this drug was out of your system completely by the 2d day after quitting altogether. It's not the drug being in your system that is the problem, it's how the brain reacts to the drug being out of your system. So the term "clean" isn't really the issue, it's probably more that your doctor wants to make sure you don't start having withdrawal symptoms, or at least that's my guess. Look, whenever you have a doctor who is being cautious with your health, bless your lucky starts and go with it, don't fight it.
Do you know how many days it´s neccesary to be without ssri medication before you start to take Wellburtin?