Does my butt keep shrinking after 6 weeks post op? (photos)

Dear zara2095,
sitting for less than 30 minutes shouldn't cause any damage to fat graft. However, prolonged pressure can cause damage. You can expect the fat tissue to shrink for the next 3 months. Also, in the early stages of recovery there is significant swelling so you can expect your butt to shrink as the swelling resolves. 
Daniel Barrett, MD, MHA, MS 

Certified, American Board of Plastic Surgery 

Member, Am. Society of Plastic Surgery

Too early to judge on the final result. You are still at the healing stage. The area in your lower back will be still bruised and swollen and this will take 8-12 weeks to settle. Wear your garment and keep your follow up with your surgeon.You have to give your body at least 12 weeks to start seeing results and final results can take 3-6 months depending the way your body heals

Congratulations on your recent surgery and thank you for sharing your question about your post operative recovery and results after your surgery.  Final results can take 6-12 months for all the swelling to subside.  At our office here at CARE we actually see all of our surgery patients the very next day after surgery and then again at two weeks and beyond. We enjoy staying closely connected to our patients and enjoy giving the extra attention and service. 
Your concerns are important to discuss directly with your board certified plastic surgeon.  He or she will appreciate the open communication and will want to help you. I hope this is helpful and wish you all the very best.  Sincerely, Brian S. Coan, MD, FACS