Happiness comes from several aspects of live and you can take small steps each day to improve one aspect of your life. Trying to do them all at once is not only overwhelming it's setting yourself up for failure. You can only do so much and that's where you need to put your focus, on small bits into the right direction. That makes things manageable and is true for all aspects of life.
One of the most important aspects is physical health. If you feel physically good about your body you also feel better about yourself mentally and emotionally. Your body actually helps you with releasing the so-called happiness hormones. Look into it and how to increase those in your life.
It will involve a good diet and exercise. And with exercise I don't mean you need to be able to run a marathon. A 15 min walk can do wonders, as can taking the stairs instead of an elevator on a regular basis. Can you add 15 minutes of walk into your day or maybe several days? If so, you're already doing more than you did and maybe you can build it up to more later on. Start small.
Same is true for making changes to your diet to eat better. Don't go overboard and change things one thing at a time. Learn to nourish yourself with cooking and meal prep is the best advice here. Learn which things are good for you and which you better can leave in the stores. Get help from a diets if you need it because we're all different and there's plenty of good info out there, but sometimes it's hard to find what's the right fit for you. Please avoid all those who tell you to use diet products and go for those who go for whole foods. The more natural, the better.
If you want to keep yourself healthy you should dive into it, because your body renews and builds itself with the stuff you put into it. Better to make it good stuff what goes in, don't you think?
Putting a smile on your face, even if you don't feel happy, also helps your body to produce the right hormones to help you feel good. The brain will register a smile via your muscles and start generating the right hormones to support that. Isn't that great?
Being in nature (for that 15 min walk for example) does the same thing. Listening to natural sounds does too. Those are elements you also easily can bring into your life a little more. See what's there and what works for you.
Meditation or mindfulness can help you with your nervousness and anxiety as well as your general well being. If you want to combine that with more physical activity you could look into doing energy arts like yoga, thai chi or chi gong.
All will teach you about breathing the right way, which like physical exercise, will bring more oxygen into your body. We need oxygen to think clearly and to stay physical healthy so maybe you should invest some time in this?
Of course you could also look into the possibilities of getting some form of therapy. There's no shame in asking for help or getting this in the form of therapy. Those people are trained to help you find new perspective and deal with past traumas.
So you see, there are a lot of things you can do to make life a little better. You don't need to have confidence for that, only the will to make a change. If you want something else you will have to start doing different things. Look at the small things you could do to make life better. I'm sure you can find a few. Start doing them, not all at once and not too many areas at the same time either. Take it slow and see how it goes. If it goes well you can add something more or do something more.
New habits take time to form so don't be mad at yourself if you have a bad day. Just give yourself a hug, tell yourself all is going to be okay, and then try again. You don't like the place where you are now so doing something new, something different is the only thing way out, right?