I need some help with positive thinking...

I am going through a pretty low time in my life emotionally at the moment, it's been going on for a while now and its destroying my marriage. My husband just cant take my mood swings and bad attitude along with negative thinking almost constantly. I have an appointment booked each with my family doctor and a counselor. I so badly want to get better as I know how depressed I am and how badly I need to change. I'm just asking for some advice on how to stay positive and train your mind to think in a more positive light every day. Anyone?