I don't know about "getting it back", maybe you should start again from the right here and right now.

Think about - and even write down the things that you love and like about yourself. If you feel doubt crawling in tell it to STFU for the moment whilst you do this. It can be anything, anything at all and as time goes on you will have more to add to the list and in this way I think your self-worth will grow. You can do a little "pump" or combat session on it every so often to build it up. After awhile you will get used to believing in yourself, rather than getting down on yourself.

Whatever you think truly about yourself the most, no one and no situation can take away from you. Because it will come from your core and that's a really hard place for things to affect.