The main character was an obese African-American girl, a teenager, who lived in a housing project in NYC. I haven’t got the slightest memory of the plot, but I remember that it had the feel of a Judy Blume book, though having delved into her bibliography I don’t think it’s one of hers.
This would have been the late 70s/early 80s, although I don’t know if the book was newly published when I read it.
If anyone figures this out on my meager information, I’ll be surprised. But thanks in advance for trying.