Living with my husband who has had depression for about 3 years

My husband has been going through a very difficult time for the last 3 years, largely started from an incident at work which severely dented his confidence. He wouldn't go to the doctor for a long time but when he realised the effect it was having on our youngest son he finally agreed to see the doctor in October and began taking Mirtazapine. The doctor has subsequently doubled the dose to 30mg but my husband feels it is not working. He was very low in the run up to Christmas and so very difficult to live with. He seems a little better at the moment, but I wondered if anyone could tell me if they have had experience of taking the same drug, how long would you expect to wait before you saw any benefits and how can you tell if it is or is not working? His mood is very cyclical anyway so I don't know if the recent better mood is anything to do with the tablets or not. He is also seeing a counsellor about once a fortnight.