Looks are transient. That is one of the first things you really realize with that first grey hair or those lines that start forming or that body that can't do all it used to. I imagine with a little sprucing up you would look just fine.
There must be more to you than your looks. Relying on them is a fools game. These bodies are designed to fail us one day.

What they are seeing is the you inside reflecting out. You aren't happy and it shows. Yes, I realize you already know that and of course it doesn't give people the right to be cruel. It is the proverbial kicking when someone is down. In reality, your family & most people are not mind readers. They don't realize how down you are, or are not smart enough to see the signs that are as plain as the nose on your face.
Shallow & sad don't you think? And you don't want to be like them, you don't seem to be.

A friend of mine says of her family, "If I wasn't related to these people, I would never have anything to do with them". And so it goes with many of us.

So, are you able to get into some sort of therapy? That might be a good place to explore body image, or changing body image.
We all have to face that someday, that we can't look young and beautiful forever. Nice idea but no, we don't get that deal.
I am one of many here who get that & for me personally it means I have to give myself a brutal & honest assessment every couple years, no matter how crappy I feel, then realign my thinking about my appearance/clothes etc. It is now about looking good, "for your age", not reliving the glory days of youth.

It sounds like you started out with a pleasant face & form and rode it as long as possible. Maybe now is the time to assess where things are today. A proper and flattering & current hair cut/style, clothes that fit you perfectly. This is underrated, and is something so important to how you look. This will give you a little boost too, and you do need a boost.
All we can do is look our best, with what we have to work with now.

There is an old song, "You're Never Fully Dressed Without A Smile", and as silly as that sounds, smiling lifts everything about your appearance, just like standing up straight, shoulders back, all the things that we were told as children apply especially now.
I wish you to find a way to feel better, about this, and all the other things that are weighing you down.