I will run over the moon
You're more aware of the sad things going on around you and have more work to do as an adult. Most people go through an existential crisis as a young adult so that may be your problem. Don't worry though. You're not alone.
Along with your age, you have increased your demands.... you want big and larger things to be equal to the world
Because you cannot erase you bad memories.
I am 15 and I'm already much less happy than I was two years ago. Listen to the song stressed out by 21 pilots I bet you can relate to it
I feel the same way. For me personally, I think it is because I feel a disconnect with anyone at this point. When you're young you are in school and around others your age. You can make friends with other kids. The other kids are generally going through the same things you are. Now, as an adult, I work with people who mostly aren't my age, not going through the same things. When you are a kid, everything is new. You are always meeting new kids, learning new things. The world was also changing more when I was a kid. We went from tapes, to CDs, then mp3s. Seemed like there was so much changing then. Also, when I was a kid I would get crushes which were kind of fun. As an adult, I don't really see anyone of interest to me. When you're a kid you just have more interests than as an adult. At least, that's how it was for me. Also, recently I've had a lot of bad experiences which have made me more jaded than I used to be. When you are a kid, you are more innocent.
I believe every age has its beauty, and happiness cant possibly come from the same things at every age and stage of your life. As you grow older your perception of life changes, you become more and more experienced. As a kid, you almost do everything for the first time, as you grow older most of the regular things arent for the first nor third time anymore. So you're pretty much accustomed to things. Your type of movie even changes, your hangout place, your music taste, your food taste.....etc.
It doesnt have to be less happy, its just a different perception, and on what your definition of happiness really is.. and most probably the things you care about or really matter to you change in time as well, but mostly it takes a little time to realize that its not that ur less happy, its just change, and its normal.
Hope that was useful ^_^
You need to make your life fun. Set goals and work towards them. I am 21 and this year I will finish my degree, then I am off travelling for a year. Finally, I will try to find a good job, meet someone, find a place of my own. Hopefully I am able to start my own business in the future, marry, have kids, own some pets and just enjoy doing the stuff I like now such as watching TV, reading, going gym, Yoga, Swimming, playing a musical instrument, eating out, going to the spa and shopping.
Be positive, remember that the glass is half full instead of half empty. You are the one who can bring and create your own happiness no matter your living, financial, relationship, etc position.
Adults in the 30's and up when you see them happy it's because of the amount of money they have . As you get older your money is suppose to grow . It's hard to be happy when you have no money .