Yes. I have found that simple meditation has helped me to become more centered. I didn’t have to take a class or study transcendental meditation. Just some simple guidelines were all that I needed.
I am 63. My growing has been done in stages over time. I’m still growing. It’s a process that lasts a lifetime if you are lucky. I was a very late bloomer and didn’t feel any confidence at all until I was in my late twenties.
Travelling all by myself one summer in Europe helped a lot. It was scared to do it, but I just bought a ticket and did it anyway.
I don’t know. I think that my belief has taught me to let go when I can’t fix things. But I didn’t have to believe in order to learn that lesson. I believe because there in something inside of me that compels me and because I have experienced the most profound understanding that I cannot put into words and that lasted for only a short time. But it was enough. And I am more relaxed sometimes because of it. More hopeful.
Exercise, especially a brisk walk.
Creativity --the kind where you get so absorbed in what you are doing that you lose track of time and forget to eat and put off going to the bathroom.
Lose yourself (find yourself) in a subject: Chess, a particular writer or philosopher, writing haiku, learning to draw, planning a trip to a country, learning a language, learning to play the balalika, taking an online course in film from Berkley, learning all you can about wolves, knitting, wabi-sabi, learn, learn, learn…
Read the essay “Self-Reliance” by Ralph Waldo Emerson. Read it again. Then read Walden by his friend Henry David Thoreau. If you get a chance, go to where they lived in Concord, Massachusetts. Visit Walden Pond.
Be of service to someone else. Maybe join Amnesty International.
One thing is most important to know. Sometimes our brain chemistry causes us to feel stress and anxiety. When that happens, it is not our fault. It is not a character flaw or a weakness. You made need medication to balance out that chemistry. No big deal. Just talk with your physician.
Anything else?
A lot of people don’t like self-help books, but I found some of them to be really good. Look for something with a title that speaks to your problem with feeling self-confident or worrying too much about what other people are thinking. Or maybe someone else in this thread can recommend something along those lines.
I will tell you that a lot of the time people are just wondering what you are thinking of them. 
Oh. One more thing. At one point when I was teaching, I had such a problem with anxiety that I kept a spray bottle of water in the regrigerator in the faculty lounge. From time to time I would just go there and spray cold water in my face. It helped! At home, I would put my face into a bowl of ice water with ice cubes. It seemed to sort of shock my system. (I got the idea from seeing Paul Newman do it in a movie – The Sting, I think.
Don’t put up with feeling bad for long without seeing your doctor, hear?