I Am Taking Lamictal 200 Mg In Adjunct With Wellbutrin

I am taking lamictal 200 mg in adjunct with Wellbutrin XL 300 mg &Cymbalta 60 mg daily. My doctor prescribed it for resistant MDD. I am the oldest of 5 in my family and we all have had long term depression/anxiety, resistant MDD. 3 of my siblings are taking lamictal and raved about how much it helped them and they recommended that I ask my psychiatrist about it. He had prescribed abilify briefly but I was worried about weight gain and EPS, so I only took it for about 1 month. He prescribed it for me and I no longer feel depressed. I have seen multiple psychiatrist over the last 20 years and I have never had symptoms of mania or hypomania, therefore no dx of Bipolar D/O for me. I was talking to my youngest sister and she said her psychiatrist told her that you (doctors) couldn't prescribe lamictal without dx of Bipolar d/o. My doctor and another one of my sisters doctor prescribed the lamictal as adjunct to antidepressants for resistant MDD. I just saw my psychiatrist and won't see again for another month, so I'm curious to know which psychiatrist is right.