Those all are, maybe, the questions that're attacking you. That's what you called self-doubt. Generally, it occurs when when you feel not confident or unable to do what you should do.
When experiencing this, you tend to panic, worry about your life. Even sometimes, you feel lost control of life.
Actually, sometimes, self-doubt is necessary. That means you understand which part of you needing to be fixed, but continuous lack of confidence can actually bring adverse effect in life. Even sometimes, it can make life full of drama.
Hesitancy makes you fearful and unmotivated. As a result, you tend to delay, not even do anything.
What causes you to doubt yourself?
Heartbreak, dismissal, broken relationship and other bad experiences, things like that make you doubt yourself of success in the future. Apparently, development in childhood affects your habit and personality. If your family made you feel inferior, you'd grow like that.
Self-doubt can arise because you're not satisfied, always look at the success of others without intending to appreciate yourself.
Well, how can you stop doubting yourself?
1. Realize that you're a self-regulating adult. Tell yourself to stop hesitating and live for the present. This will free you from the shackle of doubt that makes you afraid of the future.
2. Calm down and fill yourself with a variety of activities that evoke the sense of optimism because sometimes, you're overwhelmed by situation or emotion. Consequently, you doubt yourself.
3. Don't be afraid to ask for help from others who can support you. It could be partner, friend, mentor, etc. Tell about your condition to those who can be trusted. Surely, they'll help you.