BBL back in 2021 & aftercare wasn't great, what is this? (Photos)

Once your fat grafts are taken and mature, they behave as the rest of your fat tissue; if you gain weight your bottocks will be proportionately larger. Shape deformity, like a lump you mentioned, could be treated with lipocontouring (liposuction). Hope this helps.

Dear sarahh966_,
I understand your concern. However, without a proper assessment, it would be difficult to determine what went wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

Liposuction and fat transfer permanently change your fat distribution. Individuals who gain or lose fat, will do so based on their new fat distribution. I’m guessing you’ve probably gained some weight and it’s showing where the fat distribution currently is.
Different providers have different ideas of how this procedure should be done. Delivering consistent quality, liposuction and fat. Transfer results is more difficult than most people realized. Fat transfer can go awry with significant weight loss causing areas that were meant to be augmented to become excessively large. Consider weight loss and or revision surgery. Best,
Mats Hagstrom, MD