Not to sound like a broken record, but again you're 18, and you're in the place where life for many people is sort of a muddled mess. You're learning how to blaze your own trail apart from what you've always known and loved when you were younger, you've seen the fallibility of your parents and the community, and you are beginning to dip your toes in the "real world". I think a lot of people feel disillusionment - especially us idealistic types - because adult life is not as as it seems it will be when you're younger. It's hyped up into this magic arena of opportunity where you will do what you love and you will build a big beautiful career and you will become somebody important and you will find exactly what you were meant to be and all of that dream stuff. And then you realize that there's a lot of bullshit and criticism and difficulty and failure. And people still expect you to look at it with the same the starry eyes that you had before, and part of you wants desperately to do that, and the other part of you wonders if you'll ever find happiness again.
But, as you go, you find out that there is a small happiness to be found in the ups and downs of daily life, even though it may not be quite what you pictured, and that things do seem to sort themselves out. There's some line about how life is what happens when you're making plans, but I also think that plans tend to arise while you're busy living. If you go about whatever it is that you're going about, knowledge about what you want and what you need are going to arise as a natural consequence. I don't think you need to pretend to be happy, not in the sense that you need to stuff your feelings down while putting on a happy face. But I think what Coriolis is saying is try to do the things that make you stop thinking about happiness for a while. Get engaged, get involved, get caught up in something fun or ridiculous or difficult or puzzling. Go live some more life and forget about happiness for the moment being. Depth is inherent in life. You will find it if you are out there. And I think someone said this already, but exercise, if you're not. It basically guarantees you a period of chemically-induced happiness.