is there a difference between wellbution xl 150 and wellbution 300 er?

 As of May 08 I was on the 150 xl once a day and needed to up it. So in Sept 08, the Dr. wrote me a perscription, for wellbution 300 er to take once a day.  The pharmacist gave me the 150xl to take 2 day? I feel a bit strange, It could be my body adjusting to the new dosage this time. I was on 300 mil a day for 8 years. I was to take one  (100 ml) three times a day.  I went off the wellbution for 2 years and decided to go back on it. I have bipolpar (rapid cycler).  I want to know what the difference between them is. I don't like the idea that the pharmicist took it upon herself to give me something, that was not on the script.  She does not know my drug history of treating the disorder. It was a new pharmacy I went to. I will never go back there again. I will discuss this with my Dr too. just wanted to know. Thank you.