What's Wrong with my Butt? (photo)

For beginners, no two sides of the body/face are ever perfectly symmetric.  Nonetheless, it appears as though very careful and conservative liposuction of the lower part of the larger/longer buttock may be helpful.  Because this area requires a lot of experience to sculpt a good result, it is highly recommended to seek consultation from only a board certified plastic surgeon experienced in this area.  Glad I could help...RAS

Hello dear!
Thanks for the pictures and provided information as well.
Based on your photos, you are a good candidate for liposuction and fat transfer, to fix your problem and improve your buttocks, and I think you'll get very good results. 
l recommend you to make an in-person consultation with a board certified plastic surgeon for a proper answer and to talk about your goals and anything you need to know.
Good luck :)

Nobody is ever perfectly symetrical. It is not clear if you had surgery in the area or not. The asymetry you see is there and some judicious liposuction shoud be able to minimize the difference between each side.