I am suffered recurring depression because Dr. Diagnosed my this condition so I am taking venlafaxine 225 mg in morning and 100 mg quitpine in night before three months so now I am feeling some better but I hv noticed my sexual hv totally loss I hv discussed about my sexual problem my Dr. So he changed quetiapine medicine to mirtazapine 15 mg but when I taking mirtazapine from five days I hv very sleepy and no concentrate and again felling of depressed and anxiety please tell me this is right medicine mirtazapine replace of quetiapine please suggest me how to do m now and otherwise mirtazapine first taking symptoms this.