Had BBL 6-30-2017, last month my left buttcheek has been hurting me so bad it hurts to sit, should I go to the hospital?

Dear Alvarezbeauty,it is hard to tell what is the problem without an examination. I would suggest you to consult your plastic surgeon. Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery

You need to discuss this with the surgeon who did your BBL to make a proper assessment and treatment plan. 

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 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

You should definitely reach out to your PS as they need to see you ASAP. If they recommend going to the ER then that is what you do.