The word "gratitude" is a bit syrupy and sugary, isn't it? Sort of like smiling for no reason, it can feel forced.
Try this exercise as an alternative way to get a nice happy buzz of happiness:
1) What is something good you have in your life?
2) What if that good thing never happened? (Imagine that you missed out on meeting your significant other, or you didn't get into college, or you never got the job you have now, etc.)
When I picture my life without say, having a house to grow up in, or without having my parents in my life, or without meeting my husband, or never having met great friends, or having things go down a horrible path, it makes me feel SAD initially, but then I'm overwhelmed with feeling GRATEFUL.
Sometimes you don't realize what you have until you lose it -- how about you imagine losing it, so you can appreciate it, now. It's funny how you almost have to carve out a negative space in which to fill it with something positive. Letting sadness hit you can do just that.