Some people underestimate themselves, what is very destructive for their life and relations with surrounding world.
So, I would like to suggest you an idea how to change it and how to develop self-confidence. First of all you should admit and praise yourself for past and present victories, even if the most insignificant ones! Search for and find moments that allow you to be proud of yourself.
Make the list of all the good traits you have, for instance - I am creative person, I am optimist, I am good in sewing, cooking, etc... The list should consist at least of 20 items. Look through the list from time to time you again feel proud of yourself and add something new what you achieved or discovered in yourself...