Voice your concerns to whoever has prescribed the medication, if affects the brain chemicals but the issue is dissecting the reasons. I would always take the cautious route, write down what you have explained here and take it to the appointment. Mood fluctuations occur, we're all barraged and diving through our mind each day but having mood changes whilst on mind altering drugs is cause for concern due to the fact you are constantly under the influence of the drug and always need to be measuring its value and impact, it is important that you go to see your doctor.