I think that sometimes it's difficult to change a thought process or a behaviour that you have been using for a long time. I have also had problems with making a change, but counselling has really helped me to see things differently.
One way that I have found to be more positive is to write down one thing I have enjoyed each day. Sometimes it's really really difficult if I've had a bad day, but the more you really think in to it, the easier it becomes. Sometimes it could just be something as simple as the weather is nice, or that you spoke to someone that you really like, or something at work, but it really does help me to focus on the positives, and then you can look back at the really hard times & see that there were still small good things going on!