The creases under my butt are uneven and unpronounced. Would getting a BBL help with the creases?

Thanks for your question.A BBL will not fix the creases, but it may accentuate them due to the weight of the buttocks on the posterior thighs. Fat grafting to the creases is not very reliable.Please always consult with a board certified plastic surgeon.
Take care,
Moises Salama M.D., Board Certified Plastic Surgeon

The best way to achieve a celebrity-like butt and hips is a Brazilian Butt Lift. A Brazilian Butt Lift is a procedure where excess fat is liposuctioned from different parts of the body and moved to the buttocks. This reshapes and adds volume to the butt while keeping a natural look. Final results are permanent and generally seen about 6 months after the procedure.

Hello dear!
Thanks for the pictures and provided information as well.
Based on your photos, you are a good candidate for butt implants, to fix your problem, 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 :)

Hi. Your buttocks creases are uneven and undefined, a Lipo + BBL will get your creases define and will improve the shape and projection of your buttocks.International Member of the American Society of Plastic and Reconstructive Surgeons (ASPS)
Member of the International Society of Aesthetic Plastic Surgery (ISAPS)
Member of the International Confederation of Plastic, Reconstructive and Aesthetic Surgery (IPRAS)