Doubts, we all have them. They come to us at all times of the day or night. When they do come, you have to deal with them, or you will succumb to them.
Doubts come at you in order to keep you inside that bubble, that comfort zone.
If you start to stray (or think of straying) outside that little area that you are comfortable in (your lifestyle), then your Doubts will come for you.
When my Doubts come to me, I take it as a sign that I am doing something right, that I am making progress on my goals.
For me it my doubts (these days) are a variation on the theme that nobody will help me, and when I do achieve anything, that somehow in some way all that I have built (as in every last possession and every last dime I have) will be taken away from me (as punishment for trying to break free of my status as a Peasant).
You know . . . happy stuff like that.
It is best to keep in mind that those are your Fears. These Doubts are your Fears finding a voice to speak to you.
Your Fears are trying to keep you from harm, in their own way they see themselves as doing good. They see themselves as helping keep you in the nice safe known space that is your current lifestyle (your comfort zone).
To combat this, when your Fears come at you (masking as your Doubts) you need to start listing off all that you have accomplished and all of the skills and abilities you have.
This is to remind yourself that you have done things and are capable of a great many things. In other words . . . Confidence, specifically Confidence in yourself is what defeats your Fears and Doubts.
With them kept at bay for the moment, you can move forward onwards towards your Goals and Dreams.
As always: Keep your head up, your attitude positive, and keep moving forward!