Mirtazapine questions

Today my psychiatrist prescribed me mirtazapine 7.5mg after I reported more sleep difficulties. She's been kind of reluctant to prescribe any sedatives or anything for acute anxiety. I had never heard of it before so I came here to see what people's experiences were like and was overwhelmed by how many people said it made them gain massive amounts of weight. That's kind of the last thing I need right now, but I'm also on 300mg of wellbutrin, so I'm wondering if they balance each other out and if anyone has experience taking the two of them together? I'm also on 600mg gabapentin and 40mg propranolol. Any help is appreciated