Don't base your self-esteem on your looks, and don't compare yourself with people who are not 'real'.
The colour of your hair, the size of your clothes, the size of your boobs - there is no right or wrong. For every person who prefers brunettes, there's one who prefers red heads or blondes. For every man who likes a sporty physique, there's one who prefers bigger, or petite. For every person who prefers bigger boobs there's one who actively doesn't like them.
So, in physical terms, there is no right and wrong. There are preferences but no right or wrong.
There is nothing at all wrong with you. What is wrong is that your DP has undermined your confidence, at a time when you are vulnerable because of your pregnancy-changing body. It doesn't mean he fancies you any less, but he should be more careful and think about how it comes across to you.
It may help if you do the same. Start rating men out of 10 and wondering aloud where you could get one of them.
But seriously, try to work on your confidence - and if you need to, fake it til you make it - there is nothing so attractive as someone who is confident in their own skin. Some of the people I find most attractive are not the most attractive (not the 10/10 !) on paper, ie obviously physically. But they are confident, smiley, comfortable in who they are, don't hide themselves, don't apologise for who they are, don't compare themselves with other people.