Weight gain and Mirtazapine and stopping it for Agomelatine

[basten]

I've put on two stone (uk) in 3 months on Mirtazapine and have gone from a 14 to 18 and boobs from 36 to 40. I feel so uncomfortable and get a bit breathless now. Has anyone here stopped this drug which helped a bit with sleep and gone over to Agomelatine and if so any side effects. ??? I feel like I'm gonna explode and the weight gain has made me more depressed