I have a burning sensation in my bum 3 wks PO. Is this normal? Could it be a result of walking or sitting the way I do? (photo)

There can be some numbness that is usually temporary due the procedure. As nerves regenerate you will notice itching, followed by a burning sensation and then occasional sharp pains.Kenneth Hughes, MD, ABPS Board Certified Plastic SurgeonLos Angeles, CA

Dear sloppyfish,
I understand your concern and there is a chance that your increased activity caused burning sensation. However, without a proper assessment it would be difficult to determine what is wrong. It is best that you visit your plastic surgeon for further assessment if your issues doesn't resolve. Only after thorough examination you can get proper recommendations and advice.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Hello dear!!
Thanks for the question and provided information as well.
At the stage you are in, inflammation and discomfort are normal and might be due to the nerves regenerating. You are still early on the healing process, it can take up to six months to see your final results, so please be patient. 
If you have any concerns, please follow up close with your plastic surgeon.
Good luck :)