Anyone who is good at something, doubts they are really good at all.
There is always someone "better," "stronger," more "perfect" than we are. It is human nature to self-doubt. The one thing that not everyone has however, is resilience. The ability to keep going even under the biggest source of pressure and stress we know -ourselves.
Take those compliments you receive from people and take them to heart. Take those criticisms as well, and use them as a guideline for improvement. Take negative feedback and make it into something positive. Someone criticized the way you draw hands? They called them "fat sausages," or "lumps of mush?" Use that information to reshape how you draw hands. Knowing where your weaknesses are allows you to make them your strengths.
Just remember that you will always be your own biggest critic, so if you think you aren't doing something right, or you don't like how something is turning out, go ask someone else for their honest opinion. They might see something you don't, creating a new angle for you to tackle a project.
Everyone has self-doubt, and it isn't really something that goes away with time. Just look at the positive -It keeps us grounded and prevents us from becoming too cocky
Cheers,
WintreKitty