Been on 30mg of mirtazapine for 6 months, my mood is better on this, however, my mood has worsened in the past 2 weeks. should i increase my dose?

Maybe : Can go up to 45mg but do this in consultation with your gp as depends what other medications you're on and sometimes worth checking the mood isn't worse because of an issue other than depression (like thyroid problem etc).

Caution advised: That seems to be a fair option but before you go there, has there been any recent stress, Ill health etc. We need to be sure of other reasons of lack of response before increasing the meds are considered. Hope that helps