Was this prescribed? Generally, wellbutrin is added to an ssri to counter the weight gain and sexual side effects when the ssri is otherwise working well. Safety isn't really the issue, assuming any of these drugs can be considered "safe" as opposed to the last resort when all else failed, but whether it's the proper thing to do diagnostically depends on your symptoms and whether the Paxil is working or not.
Ask your pharmacist since they, not we, are the professional.