It sounds like having a daily walk (30 minutes) would do you a world of good. It's hard to get into the habit of doing this, but it really helps me. Just getting outside to appreciate nature's sights and sounds is beneficial. Also the vitamin D that you get from sunlight can help to pick up a persons emotions. You don't have to do much - just 30 minutes at your own pace. You can even work up to the 30 minutes over time.
Smile at someone if you get the chance - chances are - they will smile back! Now go on... take a walk.