Lost volume MONTHS after bbl, can I still fix it or do I need another surgery?

It is difficult to answer this question without assessment and knowing your expectations before the surgery 
The resorption of the fat is always difficult to predict and has to be discussed with your surgeon 
I always tell my patients that the most important thing in this procedure is the curve that we give you after the procedure by the liposuctions in the target areas.

The definitive correction for liposuction deformities requires the advanced technology of ultrasound assisted VASER liposuction. As an official trainer of VASER liposuction, I encounter suboptimal liposuction outcome referrals weekly. VASER liposuction has been the only modality that has consistently corrected liposuction caused deformities. VASER liposuction ensures a smooth contour regardless of severity of contour irregularities by virtue of being able to remove any and all remaining fat comprehensively and uniformly. Finally, when skin redundancy irregularities are observed, Renuvion technology can be simultaneously applied to tighten your skin to optimize your overall contour outcome. A Skype or FaceTime consultation with a VASER specialist will help you get an accurate recommendation and pricing.
Respectfully,
Arian Mowlavi MD, FACS
Realself 100 Hall of Fame Inductee