My first question is define happy. Do you feel
depressed over this or just unsatisfied.
I suppose you have to think hard and honestly about your spending habits. When do you buy things? Is it when you're stressed, anxious, depressed, lonely, etc? Does buying things give you a sense of self. Do you think possessing the latest and greatest makes you a more worthy person? Do you find yourself envious of what others have?
Here's another set of questions: Do you keep buying, amassing your collection so it grows bigger? Or do you sell your belongings to buy newer or better items? Do you shop compulsively or can you commit yourself not to buying things? Are you unable to afford necessities because you're spending money on things you don't need?
You don't necessarily have to answer if you don't want to, but it's something to think about.
Shopping makes people feel good- it's a neurochemically reinforced behavior. Amassing more and better stuff is evolutionarily import. The reality is, there will always be something newer, better, and more expensive. Therefore if you're always looking for the next best thing, you'll never be happy with what you have. Some people shop to cope with anxiety, depression, etc. Buying things tricks the mind into temporarily feeling satisfied. Some people may feel inferior to others use material goods to make themselves feel more important. There are all sorts of theories.
Material possession/money in itself does not buy happiness. Many studies have shown this. I have found happiness/joy/fulfillment stems more from how you live your life, rather than what you have. A few years ago I went through a very depressing period (deaths, breakups, academic stress, etc in a very short period). I spent a lot of money in a few month period seeking to quell my emotion, only to find myself just as miserable as where I had started. While that whole experience sucked, but it helped me discover how to live a satisfying life. One of the most important factors I feel is being grateful for what you do have. Perhaps start there.
There's another thread around here in the community section about happiness. You should take a look through it.
So last question. Let's say you want a new top-end Apple Watch. How will buying that make you happy? What benefit will it bring to you life? Will the function of it change your life so greatly? Will it's high monetary value make you feel like a more worthy person (literal metaphor)? Do you want dire the attention people will give you when they say "oooh he has an Apple Watch"? *