What Causes Increased Breast Tissue And Muscle Growth In Legs While On Mirtazapine?

hi ive been taking mirtazapine for just over 3 weeks now, ive started to develope breast tissue my body fat has increased greatly and my legs have started to grow in terms of muscle growth, my bum has gained more fat on it? i train 5 times a week with weights, and heavy weights. i also do cardio workouts after my muscles workouts to burn fat however this doesnt seem to do anything? im getting very worried about all this, as the breast tissue has become hard. my sex drive has depleted, and im very worried my testostrone levels are gone so far down, the female hormone now overides and im gonna start gaining more body fat as time goes on. can you advise?