I have felt like that. I was mocked by my family for having a big bum, it's big! No matter what size I was the bum was bigger than the rest of me.
I spent years hating the sight of my bum if I caught a reflection in a mirror. This started at puberty and my mother still mocks my bum at 60.
Last time she insulted me I said to her, well at least it's not sliding down the back of my legs like yours is!
Ironically my bum is extremely fashionable now and clothes are cut to fit properly and I like the look of it! I got a whistle this week when I went to take the rubbish out!
At the end of the day it's a bit ridiculous to be obsessed with how you look. I forget about my arse for a long time and only get reminded occasionally because I don't obsess over my reflection in the mirror very much.
When I do spot my bum now and again I just think, oh yes, that big bum is still there, I forgot I had that! How funny. It's been following me around all that time and I didn't notice.
Occasionally people have complained about uncomfortable seats and I pipe up with, I'm fine, I've got my own cushion with me.
Just lighten up about it. We are all a weird shape, us humans. Glamorous is a niche style, it's not how most women get through the day, it's a bit hard work if you ask me, I always pity people who have to be glammed up for work on TV etc. It's not what men have to do.
Liberate yourself from body image and as pp said, think about strength and fitness, it will serve you better in your old age. Glamour fades.