I PM'd this, but I thought I'd share it here also. I added a few things to it, so it still may be worth reading HT.
-p
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People can run into plataeus on any anti-depressant. Sometimes the doctor can tweak the dosage and that will kick start you.
*technical stuff*
The good thing about Wellbutrin SR is that it isn't specifically an SSRI. It is actually considered a NDRI, which acts on norepinephrine and Dopamine as primaries, and serotonin more secondarily. However, scientists actually don't know how it exactly works, but they know those three (or more) areas are effected. People who have problems with serotonin could have less problems with an NDRI because Serotonin is not the primary NT.
*end of technical stuff*
You also need to take into account environmental factors and short term factors. Any changes to dosage/frequency/type of medication is more long term because of needing to re-adjust to the dosage/frequency, and also the tapering off/starting up of medications, etc.
Think of it like trying to make the perfect soup with constantly changing ingredients. You can do it, but it takes the right ingredients, the right recipe, and some time.
So I guess my answer is to talk to your doctor b/c they can better assess why you are having the changes. It could be one or more things.
-p