How should I tell him ?

So after I had a baby I’ve gotten bigger I’m not at my high school weight I’m 60 plus pounds bigger I’m trying to loose weight on top of that I recently had a miscarriage at two months but my bf says comments like oh your back has gotten wider or be quiet fat face he says it in a “joking” manner but these Lowkey hurt my feelings or he’ll say I have “cooking arms” which my arms have gotten bigger I’m trying to lose weight but it’s hard but the comments hurt a bit am I being childish about it ? When I say I’m going to lose weight he says oh no I like you thicker but I don’t 🫤 that’s the thing so how should I tell him