Weight Gain on Mirtaz. Weight gain?

Hello doctors! I am suffering from sleeplessness for long time. I recently made an online consultation and I was prescribed Mirtaz 15MG with Meloset. I am getting good sleeo but I have gained 2 KG or more weight in one month after starting this medicine.This is really disgusting.  I am an active professional and I take healthy balanced diet but still I am gaining weight. I tried to reach out the doctor but she is not available. Is this weight gain inevitable? Can you suggest an alternative or a medicine for augmentation to counter weight gain? Kindly put some insights in this matter for my understanding, Do not ask for consultation directly. I will definitely consult you, if I feel like. I cannot figure out whats going on. Please advise.🙏