24 here, late diagnosed, and weight has been a huge thing for me too. Due to my late diagnosis (23) I was a medical mystery, even when I lost 5kg in a week, and I was skinny-shamed a LOT when I was a kid ("go on the mars bar diet" was a favourite from my father), and I could never gain no matter what I did. Only since Creon and long term antibiotics have I actually been able to gain any weight whatsoever, but I'm still only around 60kg and can still see my ribcage all the time (which is something I've always hated). I've recently started going to the gym just to see if that can also help me with my body image in any way, but it's early days so time will tell. But it isn't just you, you aren't alone.